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diff --git a/RFC/rfc1203.txt b/RFC/rfc1203.txt new file mode 100644 index 00000000..a362ca88 --- /dev/null +++ b/RFC/rfc1203.txt @@ -0,0 +1,2747 @@ + + + + + + +Network Working Group J. Rice +Request for Comments: 1203 Stanford +Obsoletes: RFC 1064 February 1991 + + + INTERACTIVE MAIL ACCESS PROTOCOL - VERSION 3 + +Status of this Memo + + This RFC suggests a method for workstations to access mail + dynamically from a mailbox server ("repository"). This RFC specifies + a standard for the SUMEX-AIM community and an Experimental Protocol + for the Internet community. Discussion and suggestions for + improvement are requested. Please refer to the current edition of + the "IAB Official Protocol Standards" for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Scope + + The following document is a modified version of RFC 1064, the + definition of the IMAP2 protocol. This RFC has been written + specifically as a counter proposal to RFC 1176, which itself proposes + modifications to IMAP2. Sadly, RFC 1176 was made without internal + consultation with the IMAP community, so we are in a position of + feeling we have to present a counter proposal to what, if we do not + act, will become a de facto standard. The reasons for this counter + proposal are numerous but fall mostly into the following categories: + + - IMAP2 is insufficiently powerful for a number of server/client + interactions which we believe to be important. RFC 1176 + negligibly enhances the functionality of IMAP2. + + - IMAP2 makes what we believe to be an erroneous definition for + unsolicited vs. solicited data. IMAP3 as specified herein + attempts to correct this. RFC 1176 makes no effort to remedy + these problems. + + - RFC 1176 has explicitly modified the intent of RFC 1064 by + allowing the server to make assumptions about the client's + caching architecture. We believe this to be a grave error + and do not support it in this proposal. + + - RFC 1176 specifies a number of "optional" features in the + protocol without specifying a suitable metaprotocol by which + servers and clients can adequately negotiate over the set of + implemented features. This proposal specifies a mechanism + by which servers and clients can come to an unambiguous + understanding about which features are usable by each party. + + + +Rice [Page 1] + +RFC 1203 IMAP3 February 1991 + + + + - RFC 1176 pays only lip-service to being network protocol + independent and, in fact assumes the use of TCP/IP. Neither + RFC 1064 nor this proposal make any such assumption. + + Although there are numerous other detailed objections to RFC 1176, we + believe that the above will serve to show that we believe strongly in + the importance of mailbox abstraction level mail protocols and, after + a couple of years of use of IMAP2 under RFC 1064 we believe that we + have a good enough understanding of the issues involved to be able to + take the next step. + + It is important to take this next step because of the rapid pace of + both mail system and user interface development. We believe that, + for IMAP not to die in its infancy, IMAP must be ready to respond to + emerging ISO and RFC standards in mail, such as for multi-media mail. + We believe that RFC 1176 not only provides a very small increment in + functionality over RFC 1064 but also adds a number of bugs, which + would be detrimental to the IMAP cause. Thus we propose the + following definition for IMAP3. + +Compatibility notes: + + In revising the IMAP2 protocol it has been our intent, wherever + possible to make upwards compatible changes to produce IMAP3. There + were, however, some places that had to be changed incompatibly in + order to compensate for either ambiguities in the IMAP2 protocol as + defined by RFC 1064 or behavior that proved undesirable in the light + of experience. + + It is our goal, however, that existing IMAP2 clients should still be + supported and that, at least for the foreseeable future, all IMAP3 + servers will support IMAP2 behavior as their default mode. + + The following are the major differences between this proposal, RFC + 1176 and RFC 1064: + + - In this proposal we specify a difference between "solicited" and + "unsolicited" data sent from the server. It is generally the + case that data sent by the server can be sent either in response + to an explicit request by the client or by the server of its own + volition. Any data that the server is required to sent to the + client as the result of a request is said to be solicited and + carries the same tag as the request that provoked it. Any data + sent by the server to the client that is not required by the + protocol is said to be unsolicited and carries the special "*" + tag. RFC 1176 preserves the original RFC 1064 terminology that + calls all such data sent by the server "unsolicited" even when + + + +Rice [Page 2] + +RFC 1203 IMAP3 February 1991 + + + it is, in fact, solicited. + + - This proposal introduces the experimental concept of + distinguishing between Generic, Canonical and Concrete keys, + allowing the mailbox to be viewed as a relational database + indexed by these keys. This should allow the IMAP protocol + to evolve away from its current reliance on RFC 822. RFC 1176 + does not have such a unifying model. + + - The SEARCH command has been changed so as to allow multiple + simultaneous searches to be made and to allow unsolicited + search messages to be sent by the server. Such a change is + essential to allow more sophisticated servers that can process + commands asynchronously, possibly substantially delaying + searches over slow backing storage media, for example. It is + also important to allow servers to be able to send unsolicited + search messages that might inform the client of interesting + patterns of messages, such as new and unseen mail. + + - This proposal introduces a specific protocol for the negotiation + of protocol versions and server features. This is important + because it allows client/server pairs to come to an agreement on + what behavior is really available to it. RFC 1176 introduces a + number of "optional" commands, which are in some way analogous + to "feature-introduced" commands in this proposal. The principle + distinction between these is that in RFC 1176 there is no way + for a client to discover the set of optional commands, nor is + there a way for it to determine whether a specific command + really is supported, since RFC 1176 requires the use of the + "BAD" response if a feature is not supported. There is, + therefore, no way for the client to determine why the attempted + command did not work. This also means that, for example, a + client cannot disable certain user commands or make them + invisible on menus if they are not supported, since there + is no way for the client to discover whether the commands are + indeed supported without trying to execute such a command. + + - This proposal introduces a mechanism for clients to create and + delete user flags (keywords). This is nor supported in either + RFC 1176 or RFC 1064, requiring the user to add keys manually + on the server, generally by editing some form of "init" file. + + - RFC 1064 has no mechanism for determining whether a mailbox is + readonly or not. RFC 1176 introduces a non-enforced convention + of encoding data about the readonly status of a mailbox in the + SELECT message's OK respose comment field. This is not regular + with respect to the rest of the protocol, in which the comment + field is used for no purpose other than documentation. This + + + +Rice [Page 3] + +RFC 1203 IMAP3 February 1991 + + + proposal introduces specific protocol additions for the dynamic + determination and modification of the readonly/readwrite status + of mailboxes. + +Introduction + + The intent of the Interactive Mail Access Protocol, Version 3 (IMAP3) + is to allow a (possibly unreliable) workstation or similar machine to + access electronic mail from a reliable mailbox server in an efficient + manner. + + Although different in many ways from POP2 (RFC 937), IMAP3 may be + thought of as a functional superset of POP2, and the POP2 RFC was + used as a model for this RFC. There was a cognizant reason for this; + RFC 937 deals with an identical problem and it was desirable to offer + a basis for comparison. + + Like POP2, IMAP3 specifies a means of accessing stored mail and not + of posting mail; this function is handled by a mail transfer protocol + such as SMTP (RFC 821). A comparison with the DMSP protocol of + PCMAIL can be found at the end of "System Model and Philosophy" + section. + + This protocol assumes a reliable data stream such as provided by TCP + or any similar protocol. When TCP is used, the IMAP server listens + on port 220. When CHAOS is used the IMAP server listens for the + logical contact name "IMAP3". + + Communication in IMAP is defined to be using the ASCII character + interpretation of data. Communication using other conventions may be + possible by the selection of features on some servers. + +System Model and Philosophy + + Electronic mail is a primary means of communication for the widely + spread SUMEX-AIM community. The advent of distributed workstations + is forcing a significant rethinking of the mechanisms employed to + manage such mail. With mainframes, each user tends to receive and + process mail at the computer he used most of the time, his "primary + host". The first inclination of many users when an independent + workstation is placed in front of them is to begin receiving mail at + the workstation, and, in fact, many vendors have implemented + facilities to do this. However, this approach has several + disadvantages: + + (1) Workstations (especially Lisp workstations) have a software + design that gives full control of all aspects of the system + to the user at the console. As a result, background tasks, + + + +Rice [Page 4] + +RFC 1203 IMAP3 February 1991 + + + like receiving mail, could well be kept from running for + long periods of time either because the user is asking to + use all of the machine's resources, or because, in the course + of working, the user has (perhaps accidentally) manipulated + the environment in such a way as to prevent mail reception. + This could lead to repeated failed delivery attempts by + outside agents. + + (2) The hardware failure of a single workstation could keep its + user "off the air" for a considerable time, since repair of + individual workstation units might be delayed. Given the + growing number of workstations spread throughout office + environments, quick repair would not be assured, whereas a + centralized mainframe is generally repaired very soon after + failure. + + (3) It is more difficult to keep track of mailing addresses when + each person is associated with a distinct machine. Consider + the difficulty in keeping track of a large number of postal + addresses or phone numbers, particularly if there was no + single address or phone number for an organization through + which you could reach any person in that organization. + Traditionally, electronic mail on the ARPANET involved + remembering a name and one of several "hosts" (machines) + whose name reflected the organization in which the + individual worked. This was suitable at a time when most + organizations had only one central host. It is less + satisfactory today unless the concept of a host is changed + to refer to an organizational entity and not a particular + machine. + + (4) It is very difficult to keep a multitude of heterogeneous + workstations working properly with complex mailing protocols, + making it difficult to move forward as progress is made in + electronic communication and as new standards emerge. Each + system has to worry about receiving incoming mail, routing + and delivering outgoing mail, formatting, storing, and + providing for the stability of mailboxes over a variety of + possible filing and mailing protocols. + + Consequently, while the workstation may be viewed as an Internet host + in the sense that it implements IP, it should not be viewed as the + entity which contains the user's mailbox. Rather, a mail server + machine (sometimes called a "repository") should hold the mailbox, + and the workstation (hereafter referred to as a "client") should + access the mailbox via mail transactions. Because the mail server + machine would be isolated from direct user manipulation, it could + achieve high software reliability easily, and, as a shared resource, + + + +Rice [Page 5] + +RFC 1203 IMAP3 February 1991 + + + it could achieve high hardware reliability, perhaps through + redundancy. The mail server could be used from arbitrary locations, + allowing users to read mail across campus, town, or country using + more and more commonly available clients. Furthermore, the same user + may access his mailbox from different clients at different times, and + multiple users may access the same mailbox simultaneously. + + The mail server acts an an interface among users, data storage, and + other mailers. The mail access protocol is used to retrieve + messages, access and change properties of messages, and manage + mailboxes. This differs from some approaches (e.g., Unix mail via + NFS) in that the mail access protocol is used for all message + manipulations, isolating the user and the client from all knowledge + of how the data storage is used. This means that the mail server can + utilize the data storage in whatever way is most efficient to + organize the mail in that particular environment, without having to + worry about storage representation compatibility across different + machines. + + In defining a mail access protocol, it is important to keep in mind + that the client and server form a macrosystem, in which it should be + possible to exploit the strong points of both while compensating for + each other's weaknesses. Furthermore, it's desirable to allow for a + growth path beyond the hoary text-only RFC 822 protocol. Unlike + POP2, IMAP3 has extensive features for remote searching and parsing + of messages on the server. For example, a free text search + (optionally in conjunction with other searching) can be made + throughout the entire mailbox by the server and the results made + available to the client without the client having to transfer the + entire mailbox and searching itself. Since remote parsing of a + message into a structured (and standard format) "envelope" is + available, a client can display envelope information and implement + commands such as REPLY without having any understanding of how to + parse RFC 822, etc., headers. + + Additionally, IMAP3 offers several facilities for managing a mailbox + beyond the simple "delete message" functionality of POP2. + + In spite of this, IMAP3 is a relatively simple protocol. Although + servers should implement the full set of IMAP3 functions, a simple + client can be written which uses IMAP3 in much the way as a POP2 + client. + + IMAP3 differs from the DMSP protocol of PCMAIL (RFC 1056) in a more + fundamental manner, reflecting the differing architectures of IMAP + and PCMAIL. PCMAIL is either an online ("interactive mode"), or + offline ("batch mode") system. IMAP is primarily an online system in + which real-time and simultaneous mail access were considered + + + +Rice [Page 6] + +RFC 1203 IMAP3 February 1991 + + + important. + + In PCMAIL, there is a long-term client/server relationship in which + some mailbox state is preserved on the client. There is a + registration of clients used by a particular user, and the client + keeps a set of "descriptors" for each message which summarize the + message. The server and client synchronize their states when the + DMSP connection starts up, and, if a client has not accessed the + server for a while, the client does a complete reset (reload) of its + state from the server. + + In IMAP, the client/server relationship lasts only for the duration + of the IMAP3 connection. All mailbox state is maintained on the + server. There is no registration of clients. The function of a + descriptor is handled by a structured representation of the message + "envelope". This structure makes it unnecessary for a client to know + anything about RFC 822 parsing. There is no synchronization since + the client does not remember state between IMAP3 connections. This + is not a problem since in general the client never needs the entire + state of the mailbox in a single session, therefore there isn't much + overhead in fetching the state information that is needed as it is + needed. + + There are also some functional differences between IMAP3 and DMSP. + DMSP has functions for sending messages, printing messages, and + changing passwords, all of which are done outside of IMAP3. DMSP has + 16 binary flags of which 8 are defined by the system. IMAP has flag + names; there are currently 5 defined system flag names and a facility + for some number (29 in the current implementations) of user flag + names. IMAP3 has a sophisticated message search facility in the + server to identify interesting messages based on dates, addresses, + flag status, or textual contents without compelling the client to + fetch this data for every message. + + It was felt that maintaining state on the client is advantageous only + in those cases where the client is only used by a single user, or if + there is some means on the client to restrict access to another + user's data. It can be a serious disadvantage in an environment in + which multiple users routinely use the same client, the same user + routinely uses different clients, and where there are no access + restrictions on the client. It was also observed that most user mail + access is to a relatively small set of "interesting" messages, which + were either "new" mail or mail based upon some user-selected + criteria. Consequently, IMAP3 was designed to easily identify those + "interesting" messages so that the client could fetch the state of + those messages and not those that were not "interesting". + + One crucial philosophical difference between IMAP and other common + + + +Rice [Page 7] + +RFC 1203 IMAP3 February 1991 + + + mail protocols is that IMAP is a mailbox access protocol, not a + protocol for manipulating mail files. In the IMAP model, unlike + other mail system models in which mail is stored in a linear mail + file, no specification is made for the implementation architecture + for mail storage. Servers may choose to implement mailboxes as files + but this is a detail of which the client can be totally unaware. + + What is more, in the IMAP model, mailboxes are viewed as mappings + from keys into values. There are broadly three types of keys, + generic, canonical and concrete. Generic keys are generic, mail + protocol independent keys defined by IMAP which are meaningful across + multiple mail encoding formats. An example of such a generic key + might be "TO", which would be associated with the "To:" field of an + RFC 822 format message. + + Canonical keys represent the way in which the server can associate + values that are generally "about" a certain key concept, possibly + integrating several mail format specific fields, without having to + worry the client with the particular details of any particular + message format. Thus, the canonical TO key (called $TO) could denote + anything that could reasonably be construed as being directed towards + someone. Hence, in an RFC 822 message the server could find the + union of the "To:", "Resent-To", "Apparently-To:" and "CC:" fields to + be the appropriate value associated with the canonical $TO key. + + Concrete keys allow the client to gain access to certain mail format + specific concepts, that are not pre-specified by the IMAP protocol, + in a well defined manner. For example, If the client asks for the + value associated with the "APPARENTLY-TO" key then, if the message + were to be in RFC 822 format, the server would look for a header + field called "Apparently-To:". If no such field is found or the + field is not implemented or meaningful for the particular message + format then the server will respond with the null value, called NIL, + indicating the non-existence of the field. + + Thus, IMAP servers are at liberty to implement mailboxes as a + relational databases if it seems convenient. Indeed, we anticipate + that future mail systems will tend to use database technology for the + storage and indexing of mailboxes as a result of the pressure caused + by the increasing size of mailboxes. + + Although for historical reasons IMAP is currently somewhat closely + associated with RFC 822, we anticipate that future developments in + IMAP will remove these mail format specific components and will move + towards the generic model mentioned above. This will allow IMAP more + easily to incorporate such things as multi-media mail. + + + + + +Rice [Page 8] + +RFC 1203 IMAP3 February 1991 + + +The Protocol + + The IMAP3 protocol consists of a sequence of client commands and + server responses to those commands, with extra information from the + server data being sent asynchronously to and independent to the + responses to client commands. Unlike most Internet protocols, + commands and responses are tagged. That is, a command begins with a + unique identifier (typically a short alphanumeric sequence such as a + Lisp "gensym" function would generate e.g., A0001, A0002, etc.), + called a tag. The response to this command is given the same tag + from the server. + + We distinguish between data sent by the server as the result of a + client request, which we term "SOLICITED" and data sent by the server + not as the result of a client request, which we term "UNSOLICITED". + The server may send unsolicited data at any time that would not + fragment another piece of data on the same stream rendering it + unintelligible. The server is contractually required, however, to + return all data that is solicited by the client before the return of + the completion signal for that command, i.e., all solicited data must + be returned within the temporal extent of the request/completion + acknowledgement wrapper. This does not, however, preclude the + simultaneous processing of multiple requests by the client, it simply + requires that the client be confident that it has all the requested + data when a request finishes. This allows the implementation of both + synchronous and asynchronous clients. + + Solicited data is identified by the tag of the initial request by the + client. Unsolicited data is identified by the special reserved tag + of "*". There is another special reserved tag, "+", discussed below. + + Note: the tagging of SOLICITED data is only permitted for a selected + server version other than 2.0. + + No assumptions concerning serial or monolithic processing by the + server can be made by a correct client. The server is at liberty to + process multiple requests by the same client in any order. This + allows servers to process costly searches over mailboxes on slow + backing storage media in the background, while still preserving + interactive performance. Clients can, however, assume the + serialization of the request/data/completion behavior mentioned + above. + + When a connection is opened the server sends an unsolicited OK + response as a greeting message and then waits for commands. When + commands are received the server acts on them and responds with + responses, often interspersed with data. + + + + +Rice [Page 9] + +RFC 1203 IMAP3 February 1991 + + + The client opens a connection, waits for the greeting, then sends a + LOGIN command with user name and password arguments to establish + authorization. Following an OK response from the server, the client + then sends a SELECT command to access the desired mailbox. The + user's default mailbox has a special reserved name of "INBOX" which + is independent of the operating system that the server is implemented + on. The server will generally send a list of valid flags, number of + messages, and number of messages arrived since last access for this + mailbox as solicited data, followed by an OK response. The client + may terminate access to this mailbox and access a different one with + another SELECT command. + + Because the SELECT command affects the state of the server in a + fundamental way, the server is required to process all outstanding + commands for any given mailbox before sending the OK tag for the + SELECT command. Thus, the client will always know that all responses + before an OK SELECT response will refer to the old mailbox and all + responses following it will apply to the new mailbox. + + Because, in the real world, local needs or experimental work will + dictate that servers will support both supersets of the defined + behavior and incompatible changes, servers will support a + SELECT.VERSION command and a SELECT.FEATURES command, the purpose of + which is to allow clients to select the overall behavior and specific + features that they want from a server. The default behavior of any + server is to process commands and to have interaction syntax the same + as is specified by IMAP2 in RFC 1064. A server may not behave in any + other manner unless the SELECT.VERSION or SELECT.FEATURES commands + are used to select different behavior. + + Over time, when groups of generally useful changes to the current, + default behavior of the server are found, these will be collected + together and incorporated in such a way that all of the features can + be selected simply by selecting a particular major version number of + the protocol. It should be noted that the version numbers (both + major and minor) selected by the SELECT.VERSION command denote + versions of the IMAP protocol, not versions of the server per se. + Thus, although in general changes to the protocol specification will + be made in such a way that they are upwards compatible, this cannot + be guaranteed. No client should rely on tests of the form "if + major_version > 2 then..." being valid for all protocol versions, + since incompatible changes might be made in the future. + + The client reads mailbox information by means of FETCH commands. The + actual data is transmitted via the solicited data mechanism (that is, + FETCH should be viewed as poking the server to include the desired + data along with any other data it wishes to transmit to the client). + There are three major categories of data which may be fetched. + + + +Rice [Page 10] + +RFC 1203 IMAP3 February 1991 + + + The first category is that data which is associated with a message as + an entity in the mailbox. There are presently three such items of + data: the "internal date", the "RFC 822 size", and the "flags". The + internal date is the date and time that the message was placed in the + mailbox. The RFC 822 size is subject to deletion in the future; it + is the size in bytes of the message, expressed as an RFC 822 text + string. Current clients only use it as part of a status display + line. The flags are a list of status flags associated with the + message (see below). All of the first category data can be fetched + by using the macro-fetch word "FAST"; that is, "FAST" expands to + "(FLAGS INTERNALDATE RFC822.SIZE)". + + The second category is that data which describes the composition and + delivery information of a message; that is, information such as the + message sender, recipient lists, message-ID, subject, etc. This is + the information which is stored in the message header in RFC 822 + format message and is traditionally called the "envelope". [Note: + this should not be confused with the SMTP (RFC 821) envelope, which + is strictly limited to delivery information.] IMAP3 defines a + structured and unambiguous representation for the envelope which is + particularly nice for Lisp-based parsers. A client can use the + envelope for operations such as replying and not worry about RFC 822 + at all. Envelopes are discussed in more detail below. The first and + second category data can be fetched together by using the macro-fetch + word "ALL"; that is, "ALL" expands to "(FLAGS INTERNALDATE + RFC822.SIZE ENVELOPE)". + + The third category is that data which is intended for direct human + viewing. The present RFC 822 based IMAP3 defines three such items: + RFC822.HEADER, RFC822.TEXT, and RFC822 (the latter being the two + former appended together in a single text string). Fetching "RFC822" + is equivalent to typing the RFC 822 representation of the message as + stored on the mailbox without any filtering or processing. + + Typically, a client will "FETCH ALL" for some or all of the messages + in the mailbox for use as a presentation menu, and when the user + wishes to read a particular message will "FETCH RFC822.TEXT" to get + the message body. A more primitive client could, of course, simply + "FETCH RFC822" a la POP2-type functionality. + + The client can alter certain data by means of a STORE command. As an + example, a message is deleted from a mailbox by a STORE command which + includes the \DELETED flag as one of the flags being set. + + Other client operations include copying a message to another mailbox + (COPY command), permanently removing deleted messages (EXPUNGE + command), checking for new messages (CHECK command), and searching + for messages which match certain criteria (SEARCH command). + + + +Rice [Page 11] + +RFC 1203 IMAP3 February 1991 + + + The client terminates the session with the LOGOUT command. The + server returns a "BYE" followed by an "OK". + +A Typical Scenario + + Client Server + ------ ------ + {Wait for Connection} + {Open Connection} --> + <-- * OK IMAP3 Server Ready + {Wait for command} + A001 SUPPORTED.VERSIONS --> + <-- * SUPPORTED.VERSIONS ((2 0 ) + (3 0 EIGHT.BIT.TRANSPARENT + AUTO.SET.SEEN + TAGGED.SOLICITED)) + A001 OK Supported Versions returned. + {Wait for command} + A002 SELECT.VERSION (3 0) --> + <-- A002 OK Version 3.0 Selected. + {Wait for command} + A002 SELECT.FEATURES TAGGED.SOLICITED --> + <-- A002 OK Features selected. + {Wait for command} + A003 LOGIN Fred Secret --> + <-- A003 OK User Fred logged in + {Wait for command} + A004 SELECT INBOX --> + <-- A004 FLAGS (Meeting Notice \Answered + \Flagged \Deleted \Seen) + <-- A004 19 EXISTS + <-- A004 2 RECENT + <-- A004 OK Select complete + {Wait for command} + A005 FETCH 1:19 ALL --> + <-- A005 1 Fetch (......) + ... + <-- A005 18 Fetch (......) + <-- A005 19 Fetch (......) + <-- A005 OK Fetch complete + {Wait for command} + A006 FETCH 8 RFC822.TEXT --> + <-- A006 8 Fetch (RFC822.TEXT {893} + ...893 characters of text... + <-- ) + <-- A006 OK Fetch complete + {Wait for command} + + + + +Rice [Page 12] + +RFC 1203 IMAP3 February 1991 + + + A007 STORE 8 +Flags \Deleted --> + <-- A007 8 Store (Flags (\Deleted + \Seen)) + <-- A007 OK Store complete + {Wait for command} + A008 EXPUNGE --> + <-- A008 19 EXISTS + <-- A008 8 EXPUNGE + <-- A008 18 EXISTS + <-- A008 Expunge complete + {Wait for command} + A009 LOGOUT --> + <-- A009 BYE IMAP3 server quitting + <-- A009 OK Logout complete + {Close Connection} --><-- {Close connection} + {Go back to start} + + A more complex scenario produced by a pipelining multiprocess client. + + Client Server + ------ ------ + {Wait for Connection} + {Open session as above} + <-- A004 19 EXISTS + <-- A004 2 RECENT + <-- A004 OK Select complete + {Wait for command} + A005 SEARCH RECENT --> + <-- A005 SEARCH (18 19) (RECENT) + <---A005 OK Search complete + A006 FETCH 18:19 ALL RFC822.TEXT + A007 STORE 18:19 +FLAGS (\SEEN) + A008 FETCH 1:17 ALL --> + <-- A006 18 Fetch (... RFC822.TEXT ...) + A009 STORE 18 +FLAGS (\DELETED) + <-- A006 19 Fetch (... RFC822.TEXT ...) + <-- A006 OK Fetch complete + <-- A007 18 STORE (Flags (\Seen)) + A010 STORE 19 +FLAGS (\DELETED) + <-- A007 19 STORE (Flags (\Seen)) + <-- A007 OK Store complete + <-- A008 1 Fetch (......) + ... + <-- A008 16 Fetch (......) + <-- A008 17 Fetch (......) + <-- A008 OK Fetch complete + <-- A009 18 STORE (Flags (\Seen + \Deleted)) + + + +Rice [Page 13] + +RFC 1203 IMAP3 February 1991 + + + <-- A009 OK Store complete + <-- A010 19 STORE (Flags (\Seen + \Deleted)) + <-- A010 OK Store complete + {Wait for command} + <-- * EXISTS 23 + <-- * RECENT 4 + <-- * SEARCH (20 21 22 23) (RECENT) + A011 FETCH 20:23 ALL RFC822.TEXT + +Conventions + + The following terms are used in a meta-sense in the syntax + specification below: + + An ASCII-STRING is a sequence of arbitrary ASCII characters. + + An ATOM is a sequence of ASCII characters delimited by SP or CRLF. + + A CHARACTER is any ASCII character except """", "{", CR, LF, "%", + or "\". + + A CRLF is an ASCII carriage-return character followed immediately + by an ASCII linefeed character. + + A NUMBER is a sequence of the ASCII characters which represent + decimal numerals ("0" through "9"), delimited by SP, CRLF, ",", or + ":". + + A SP is the ASCII space character. + + A TEXT_LINE is a human-readable sequence of ASCII characters up to + but not including a terminating CRLF. + + One of the most common fields in the IMAP3 protocol is a STRING, + which may be an ATOM, QUOTED-STRING (a sequence of CHARACTERs inside + double-quotes), or a LITERAL. A literal consists of an open brace + ("{"), a number, a close brace ("}"), a CRLF, and then an ASCII- + STRING of n characters, where n is the value of the number inside the + brace. In general, a string should be represented as an ATOM or + QUOTED-STRING if at all possible. The semantics for QUOTED-STRING or + LITERAL are checked before those for ATOM; therefore an ATOM used in + a STRING may only contain CHARACTERs. Literals are most often sent + from the server to the client; in the rare case of a client to server + literal there is a special consideration (see the "+ text" response + below). + + Another important field is the SEQUENCE, which identifies a set of + + + +Rice [Page 14] + +RFC 1203 IMAP3 February 1991 + + + messages by consecutive numbers from 1 to n where n is the number of + messages in the mailbox. A sequence may consist of a single number, + a pair of numbers delimited by colon indicating all numbers between + those two numbers, or a list of single numbers and/or number pairs. + For example, the sequence 2,4:7,9,12:15 is equivalent to + 2,4,5,6,7,9,12,13,14,15 and identifies all of those messages. + +Definitions of Commands and Responses + + Summary of Commands and Responses + +Commands: + tag NOOP + tag LOGIN user password + tag LOGOUT + tag SELECT mailbox + tag CHECK + tag EXPUNGE + tag COPY sequence mailbox + tag FETCH sequence data + tag STORE sequence data value + tag SEARCH criteria + tag BBOARD bboard + tag FIND (BBOARDS / MAILBOXES) pattern + tag READONLY + tag READWRITE + tag SELECT.VERSION (major_version minor_version) + tag SELECT.FEATURES features + tag SUPPORTED.VERSIONS + tag FLAGS + tag SET.FLAGS + +Responses (can be either solicited or unsolicited): + */tag FLAGS flag_list + */tag SEARCH (numbers) (criteria) + */tag EXISTS + */tag RECENT + */tag EXPUNGE + */tag STORE data + */tag FETCH data + */tag BBOARD bboard_name + */tag MAILBOX non_inbox_mailbox_name + */tag SUPPORTED.VERSIONS version_data + */tag READONLY + */tag READWRITE + */tag OK text + */tag NO text + */tag BAD text + + + +Rice [Page 15] + +RFC 1203 IMAP3 February 1991 + + + */tag BYE text + +Responses (can only be solicited): + tag COPY message_number + +Responses (can only be unsolicited): + + text + +Commands + + tag NOOP + + The NOOP command returns an OK to the client. By itself, it does + nothing, but certain things may happen as side effects. For + example, server implementations which implicitly check the mailbox + for new mail may do so as a result of this command. The primary + use of this command is to for the client to see if the server is + still alive (and notify the server that the client is still alive, + for those servers which have inactivity autologout timers). + + tag LOGIN user password + + The LOGIN command identifies the user to the server and carries + the password authenticating this user. This information is used + by the server to control access to the mailboxes. + + EXAMPLE: A001 LOGIN SMITH SESAME logs in as user SMITH with + password SESAME. + + tag LOGOUT + + The LOGOUT command indicates the client is done with the session. + The server sends a solicited BYE response before the (tagged) OK + response, and then closes the connection. + + tag SELECT mailbox + + The SELECT command selects a particular mailbox. The server must + check that the user is permitted read access to this mailbox. + Prior to returning an OK to the client, the server must send an + solicited FLAGS and <n> EXISTS response to the client giving the + flags list for this mailbox (simply the system flags if this + mailbox doesn't have any special flags) and the number of messages + in the mailbox. It is also recommended that the server send a <n> + RECENT unsolicited response to the client for the benefit of + clients which make use of the number of new messages in a mailbox. + It is further recommended that servers should send an unsolicited + READONLY message if the mailbox that has been selected is not + + + +Rice [Page 16] + +RFC 1203 IMAP3 February 1991 + + + writable by the user. + + Multiple SELECT commands are permitted in a session, in which case + the prior mailbox is deselected first. + + The default mailbox for the SELECT command is INBOX, which is a + special name reserved to mean "the primary mailbox for this user + on this server". The format of other mailbox names is operating + system dependent (as of this writing, it reflects the path of the + mailbox on the current servers), though it could reflect any + server-specific naming convention for the namespace of mailboxes. + Such a namespace need not and should not be viewed as being + equivalent or linked to the server machine's file system. + + EXAMPLES: A002 SELECT INBOX ;; selects the default mailbox. + A002 197 EXISTS ;; server says 197 messages in INBOX + A002 5 RECENT ;; server says 5 are recent. + A002 OK Select complete. + or + A003 SELECT /usr/fred/my-mail.txt + ;; select a different user specified mailbox. + ... + + tag CHECK + + The CHECK command forces a check for new messages and a rescan of + the mailbox for internal change for those implementations which + allow multiple simultaneous read/write access to the same mailbox + (e.g., TOPS-20). It is recommend that periodic implicit checks + for new mail be done by servers as well. The server must send a + solicited <n> EXISTS response prior to returning an OK to the + client. + + tag EXPUNGE + + The EXPUNGE command permanently removes all messages with the + \DELETED flag set in its flags from the mailbox. Prior to + returning an OK to the client, for each message which is removed, + a solicited <n> EXPUNGE response is sent indicating which message + was removed. The message number of each subsequent message in the + mailbox is immediately decremented by 1; this means that if the + last 5 messages in a 9-message mailbox are expunged you will + receive 5 "5 EXPUNGE" responses for message 5. To ensure mailbox + integrity and server/client synchronization, it is recommended + that the server do an implicit check prior to commencing the + expunge and again when the expunge is completed. Furthermore, if + the server allows multiple simultaneous access to the same mailbox + the server must guarantee both the integrity of the mailbox and + + + +Rice [Page 17] + +RFC 1203 IMAP3 February 1991 + + + the views of it held by the clients. + + EXPUNGE is not allowed if the user does not have write access to + this mailbox. If a user does not have write access to the mailbox + then the server is required to signal this fact by replying with a + NO response with a suitable text string that can be presented to + the user explaining that the mailbox is read-only. It is further + recommended that servers send an unsolicited READONLY message to + clients that attempt an expunge operation on a read only mailbox. + + tag COPY sequence mailbox + + The COPY command copies the specified message(s) to the specified + destination mailbox. If the destination mailbox does not exist, + the server should create it. Prior to returning an OK to the + client, the server must return a solicited <n> COPY response for + each message copied. + + EXAMPLE: A003 COPY 2:4 MEETING copies messages 2, 3, and 4 to + mailbox "MEETING". + + COPY is not allowed if the user does not have write access to the + destination mailbox. If a user does not have write access to the + destination mailbox then the server is required to signal this + fact by replying with a NO response with a suitable text string + that can be presented to the user explaining that the mailbox is + read-only. It is further recommended that servers send an + unsolicited READONLY message to clients that attempt to copy to a + read only mailbox. IMAP3 does not specify "where" the message + will be put in the mailbox to which it has been copied. + + tag FETCH sequence fetch_att + + The FETCH command retrieves data associated with a message in the + mailbox. The data items to be fetched may be either a single atom + or an S-expression list. The attributes that can be fetched are + any of those mentioned specifically below along with any generic, + canonical or concrete key. The set of predefined generic keys is: + {BCC, BODY, CC, FROM, HEADER, SIZE, SUBJECT, TEXT, TO}. The set + of predefined canonical keys is {$CC, $FROM, $SUBJECT, $TO}. The + value returned by the server for a non-existent or non-meaningful + key is defined to be the null value, NIL. + + ALL Equivalent to: + (FLAGS INTERNALDATE RFC822.SIZE ENVELOPE) + + ENVELOPE The envelope of the message. The envelope is + computed by the server by parsing the header, + + + +Rice [Page 18] + +RFC 1203 IMAP3 February 1991 + + + i.e., the RFC 822 header for an RFC822 format + message, into the component parts, defaulting + various fields as necessary. + + FAST Macro equivalent to: + (FLAGS INTERNALDATE RFC822.SIZE) + + FLAGS The flags which are set for this message. + This may include the following system flags: + + \RECENT Message arrived since + last read of this mailbox + \SEEN Message has been read + \ANSWERED Message has been answered + \FLAGGED Message is "flagged" for + urgent/special attention + \DELETED Message is "deleted" for + removal by later EXPUNGE + + INTERNALDATE The date and time the message was written to + the mailbox. + + RFC822 The message in RFC 822 format. + + RFC822.HEADER The RFC 822 format header of the message. + + RFC822.SIZE The number of characters in the message as + expressed in RFC 822 format. + + RFC822.TEXT The text body of the message, omitting the + RFC 822 header. + + EXAMPLES: + + A003 FETCH 2:4 ALL + fetches the flags, internal date, RFC 822 size, and envelope + for messages 2, 3, and 4. + + A004 FETCH 3 RFC822 + fetches the RFC 822 representation for message 3. + + A005 FETCH 4 (FLAGS RFC822.HEADER) + fetches the flags and RFC 822 format header for message 4. + + A006 FETCH 42 $SUBJECT + A006 FETCH $SUBJECT "Some subject text..." + A006 OK FETCH completed ok. + fetches the canonical subject field. + + + +Rice [Page 19] + +RFC 1203 IMAP3 February 1991 + + + A007 FETCH 42 APPARENTLY-TO + A007 FETCH APPARENTLY-TO NIL + A007 OK FETCH found no value. + fetches the concrete apparently-to field. + + tag STORE sequence data value + + The STORE command alters the values associated with particular + keys for a message in the mailbox. As is the case for the FETCH + command, any generic, canonical or concrete key may be used to + index the value provided. In addition to these, the following + pre-defined keys are provided. + + FLAGS Replace the flags for the message with the + argument (in flag list format). + The server must respond with a solicited STORE FLAGS + message, showing the new state of the flags after + the store. + + +FLAGS Add the flags in the argument to the + message's flag list. + The server must respond with a solicited STORE FLAGS + message, showing the new state of the flags after + the store. + + -FLAGS Remove the flags in the argument from the + message's flag list. + The server must respond with a solicited STORE FLAGS + message, showing the new state of the flags after + the store. + + RFC822.HEADER Replace the header of the message(s) with that + specified. This allows users to use their mailboxes + as databases with header fields as keys. + The server must respond with solicited + STORE RFC822.HEADER, STORE RFC822.SIZE and + STORE ENVELOPE messages, showing the new state + of the reparsed header after the store. + + RFC822.TEXT Replace the body of the messages with that specified. + The server must respond with solicited + STORE RFC822.TEXT and STORE RFC822.SIZE messages, + showing the new state of the message after the store. + + STORE is not allowed if the user does not have write access to + this mailbox. + + The server is required to send a solicited STORE response for + + + +Rice [Page 20] + +RFC 1203 IMAP3 February 1991 + + + each store operation that results in a format transformation by + the server. For example, the server is required to send a + STORE FLAGS response when the client performs a STORE +FLAGS or + a STORE -FLAGS, since the client may not easily be able to know + what the result of this command will be. Similarly, if the + client emits a STORE FROM command then the server should + respond with a suitable STORE FROM response because the client + would be sending a string value to be stored and the server + should transform this into a set of addresses. In general, + however, although it is legal for the server to send a + solicited STORE response for each STORE operation, this is + discouraged, since it might result in the retransmission of + very large and unnecessary amounts of data that have been + stored. + + EXAMPLE: A003 STORE 2:4 +FLAGS (\DELETED) marks messages 2, 3, + and 4 for deletion. + + tag SEARCH search_criteria + + The SEARCH command searches the mailbox for messages which match + the given set of criteria. The server response SEARCH (criteria) + (numbers) gives the set of messages which match the conjunction of + the criteria specified. In addition to each of the search + criteria there is its logical inverse. The logical inverse + criterion is denoted by the ~ (tilda) sign. + + Thus, no message that matches the criterion: + FROM crispin + + will match the criterion: + ~FROM crispin + + The criteria for the search can be any generic, canonical or + concrete key. In addition to these, the following pre-defined + keys are also provided: + + ALL All messages in the mailbox; the default + initial criterion for ANDing. + + ANSWERED Messages with the \ANSWERED flag set. + + BCC string Messages which contain the specified string + in the envelope's BCC field. + + BEFORE date Messages whose internal date is earlier than + the specified date. + + + + +Rice [Page 21] + +RFC 1203 IMAP3 February 1991 + + + BODY string Messages which contain the specified string + in the body of the message. + + CC string Messages which contain the specified string + in the envelope's CC field. + + DELETED Messages with the \DELETED flag set. + + FLAGGED Messages with the \FLAGGED flag set. + + FROM string Messages which contain the specified string + in the envelope's FROM field. + + HEADER string Messages which contain the specified string + in the message header. + + KEYWORD flag Messages with the specified flag set. + + NEW Messages which have the \RECENT flag set but + not the \SEEN flag. This is functionally + equivalent to "RECENT UNSEEN". + + OLD Messages which do not have the \RECENT flag + set. + + ON date Messages whose internal date is the same as + the specified date. + + RECENT Messages which have the \RECENT flag set. + + SEEN Messages which have the \SEEN flag set. + + SINCE date Messages whose internal date is later than + the specified date. + + SUBJECT string Messages which contain the specified string + in the envelope's SUBJECT field. + + TEXT string Messages which contain the specified string. + + TO string Messages which contain the specified string in + the envelope's TO field. + + EXAMPLE: A003 SEARCH DELETED FROM "SMITH" SINCE 1-OCT-87 + returns the message numbers for all deleted messages from Smith + that were placed in the mailbox since October 1, 1987. + + Implementation note: The UNANSWERED, UNDELETED, UNFLAGGED, + + + +Rice [Page 22] + +RFC 1203 IMAP3 February 1991 + + + UNKEYWORD and UNSEEN criteria, described below, are preserved in + IMAP3 for IMAP2 compatibility. They are, however, considered + obsolete and new Client programs are encouraged to use the ~ + notation for the logical inverses of search criteria with a view + to the dropping of this outmoded syntax in later versions. + + UNANSWERED Messages which do not have the \ANSWERED flag + set. + + UNDELETED Messages which do not have the \DELETED flag + set. + + UNFLAGGED Messages which do not have the \FLAGGED flag + set. + + UNKEYWORD flag Messages which do not have the specified flag + set. + + UNSEEN Messages which do not have the \SEEN flag set. + + tag READONLY + + The READONLY command indicates that the client wishes to make the + mailbox read-only. The server is required to reply with a + solicited READONLY or READWRITE response. + + tag READWRITE + + The READWRITE command indicates that the client wishes to make the + mailbox read-write. The server is required to reply with a + solicited READONLY or READWRITE response. + + tag SUPPORTED.VERSIONS + + The SUPPORTED.VERSIONS solicits from the server a + SUPPORTED.VERSIONS message, which encapsulates information about + which versions and features the server supports. + + tag SELECT.VERSION (major_version minor_version) + + The SELECT.VERSION command indicates that the client wishes to + select certain behavior on the part of the server. The major and + minor versions indicate the specific version of the protocol being + selected. + + EXAMPLE: A002 SELECT.VERSION (3 0) + + A client may not request a server version that is not supported by + + + +Rice [Page 23] + +RFC 1203 IMAP3 February 1991 + + + the server, i.e., which is specifically mentioned in the response + to a SUPPORTED.VERSIONS command. An attempt to do so by a client + will result in a NO response from the server. It is an error for + the SELECT.VERSION command to be used after a mailbox has been + selected. The rationale for this is that for some server + implementations it might be necessary to spawn separate programs + to implement widely divergent protocol versions. Thus, the client + cannot be allowed to expect any server state to be preserved after + the use of the SELECT.VERSION command. The default version of all + servers is 2.0, i.e., IMAP2 as defined by RFC 1064. + + tag SELECT.FEATURES 1#features + + The SELECT.FEATURES command indicates that the client wishes to + select certain specific features on the part of the server. A + client may not request a feature that is not supported by the + server, i.e., one that is explicitly mentioned in the set of + features for the selected version returned by the + SUPPORTED.VERSIONS command. An attempt to do so by a client will + result in a NO response from the server. + + EXAMPLE: A002 SELECT.FEATURES AUTO.SET.SEEN ~TAGGED.SOLICITED + EIGHT.BIT.TRANSPARENT + + i.e., select the set of features called AUTO.SET.SEEN and + EIGHT.BIT.TRANSPARENT and deselect the feature called + TAGGED.SOLICITED. The use of the SELECT.FEATURES command + completely resets the set of selected features. Note: These are + only example feature names and are not necessarily supported by + any server. See the appendix on features for more information on + features. Note: Some features, when present in the server, will + cause the upwards compatible extension of the grammar, i.e., by + adding extra commands. The server is at liberty not to remove + these upwards compatible extensions to the command tables when a + feature is disabled. Thus, it is an error for a client to rely on + getting a NO or BAD response in any way, for instance to determine + the selectedness or presence of a feature. + + tag BBOARD bboard + + The BBOARD command is equivalent to SELECT, except that its + argument is a bulletin board (BBoard) name. The format of a + BBoard name is implementation specific, although it is strongly + encouraged to use something that resembles a name in a generic + sense and not a file or mailbox name on the particular system. + There is no requirement that a BBoard name be a mailbox name or a + file name (in particular, Unix netnews has a completely different + namespace from mailbox or file names). + + + +Rice [Page 24] + +RFC 1203 IMAP3 February 1991 + + + The result from the BBOARD command is identical from that of the + SELECT command. For example, in the TOPS-20 server + implementation, the command + A0002 BBOARD FOO + is exactly equivalent to the command + A0002 SELECT POBOX:<BBOARD>FOO.TXT + Note: the equivalence in this example is *not* required by the + protocol, and merely reflects the fuzzy distinction between + mailboxes and BBoards on TOPS-20. + + tag FIND (BBOARDS / MAILBOXES) pattern + + The FIND command accepts as arguments the keywords BBOARDS or + MAILBOXES and a pattern which specifies some set of BBoard/mailbox + names which are usable by the BBOARD/SELECT command. Two wildcard + characters are defined; "*" specifies that any number (including + zero) characters may match at this position and "%" specifies that + a single character may match at this position. For example, + FOO*BAR will match FOOBAR, FOOD.ON.THE.BAR and FOO.BAR, whereas + FOO%BAR will match only FOO.BAR; furthermore, "*" will match all + BBoards/mailboxes. The following quoting convention applies to + wildcards: "\*" is the literal "*" character, "\%" is the literal + "%" character and "\\" is the literal "\" character. Notes: The + format of mailboxes is server implementation dependent. The + special mailbox name INBOX is not included in the output to the + FIND MAILBOXES command. + + The FIND command solicits any number of BBOARD or MAILBOX + responses from the server as appropriate. + + Examples: + A0002 FIND BBOARDS * + A0002 BBOARD FOOBAR + A0002 BBOARD GENERAL + A0002 OK FIND completed + or + A0002 FIND MAILBOXES FOO%BA* + A0002 MAILBOX FOO.BAR + A0002 MAILBOX FOO.BAZZAR + A0002 OK FIND completed + + Note: Although the use of explicit file or path names for + mailboxes is discouraged by this standard, it may be unavoidable. + It is important that the value returned in the MAILBOX solicited + reply be usable in the SELECT command without remembering any path + specification which may have been used in the FIND MAILBOXES + pattern. + + + + +Rice [Page 25] + +RFC 1203 IMAP3 February 1991 + + + tag FLAGS + + The FLAGS command solicits a FLAGS response from the server. + + tag SET.FLAGS flag_list + + The SET.FLAGS command defines the user specifiable flags for this + mailbox, i.e., the keywords. If this set does not include flags + formerly sent to the client by the server in a FLAGS message then + this constitutes a request to delete the flag. Any new flags + should be created. This command does not affect the system + defined flags and any system flags that are included in the + flag_list will be ignored. The server must respond to this + command with a solicited FLAGS message. If the deletion of a flag + results in the invalidation of the flag sets of any messages then + the server is required to send solicited STORE FLAGS messages to + the client for each modified message. + +Responses: + + */tag OK text + + In its solicited form this response identifies successful + completion of the command with the indicated tag. The text is a + line of human-readable text which may be useful in a protocol + telemetry log for debugging purposes. + + In its unsolicited form, this response indicates simply that the + server is alive. No special action on the part of the client is + called for. This is presently only used by servers at startup as + a greeting message indicating that they are ready to accept the + first command. This usage, although legal, is by no means + required. The text is a line of human-readable text which may be + logged in protocol telemetry. + + */tag NO text + + In its solicited form this response identifies unsuccessful + completion of the command with the indicated tag. The text is a + line of human-readable text which probably should be displayed to + the user in an error report by the client. + + In its unsolicited form this response indicates some operational + error at the server which cannot be traced to any protocol + command. The text is a line of human-readable text which should + be logged in protocol telemetry for the maintainer of the server + and/or the client. + + + + +Rice [Page 26] + +RFC 1203 IMAP3 February 1991 + + + */tag BAD text + + In its solicited form response indicates faulty protocol received + from the client and indicates a bug. The text is a line of + human-readable text which should be recorded in any telemetry as + part of a bug report to the maintainer of the client. + + In its unsolicited form response indicates some protocol error at + the server which cannot be traced to any protocol command. The + text is a line of human-readable text which should be logged in + protocol telemetry for the maintainer of the server and/or the + client. This generally indicates a protocol synchronization + problem, and examination of the protocol telemetry is advised to + determine the cause of the problem. + + */tag BYE text + + This indicates that the server is about to close the connection. + The text is a line of human-readable text which should be + displayed to the user in a status report by the client. IMAP2 + requires that the server emit a solicited BYE response as part of + a normal logout sequence. This solicited form is not required + under IMAP3, though is still legal for compatibility. In its + unsolicited form the BYE response is used as a panic shutdown + announcement by the server. It is required to be used by any + server which performs autologouts due to inactivity. + + */tag number message_data + + The solicited (tag number message_data) response is generated as + the result of a number of client requests. The server may also + emit any the following at any time as unsolicited data (i.e., * + number message_data). The message_data is one of the following: + + EXISTS The specified number of messages exists in the mailbox. + + RECENT The specified number of messages have arrived since the + last time this mailbox was selected with the SELECT + command or equivalent. + + EXPUNGE The specified message number has been permanently + removed from the mailbox, and the next message in the + mailbox (if any) becomes that message number. + The server must send a solicited EXPUNGE response + for each message that it expunges as the result + of an EXPUNGE command. Note: future versions of the + protocol may allow the use of a message sequence + as a value returned by the EXPUNGE response to allow the + + + +Rice [Page 27] + +RFC 1203 IMAP3 February 1991 + + + more efficient compaction of client representations of + mailboxes. + + STORE data + Functionally equivalent to FETCH, only it is sent by the + server when the state of a mailbox changes. The server + must send solicited STORE responses as the result of + any change caused by a STORE command. + + FETCH data + This is the principle means by which data about a + message is sent to the client. The data is in a + Lisp-like S-expression property list form. Just as the + FETCH request from the client can fetch any generic, + canonical or concrete key, so also the FETCH response + can return values for any of these keys as well as for + the pre-defined attributes mentioned below. Note that + the server is permitted to send any unsolicited FETCH + or STORE messages that it should choose, be they the + values associated with generic, canonical or concrete + keys. Clients are required to ignore any such + FETCH responses that it cannot interpret. For example, + clients are not required to be able to understand, i.e., + use fruitfully, the canonical $TO key, but they are + required to be able to ignore an unsolicited $TO message + correctly. + + ENVELOPE An S-expression format list which describes the + envelope of a message. The envelope is computed + by the server by parsing the RFC 822 header into + the component parts, defaulting various fields + as necessary. + + The fields of the envelope are in the following + order: date, subject, from, sender, reply-to, to, + cc, bcc, in-reply-to, and message-id. The date, + subject, in-reply-to, and message-id fields are + strings. The from, sender, reply-to, to, cc, + and bcc fields are lists of addresses. + + An address is an S-expression format list which + describes an electronic mail address. The fields + of an address are in the following order: + personal name, source-route (i.e., the + at-domain-list in SMTP), mailbox name, host name + and comments. Implementation note: The addition + of the comment field is an incompatible extension + from IMAP2. The server is required not to provide + + + +Rice [Page 28] + +RFC 1203 IMAP3 February 1991 + + + this field when running in IMAP2 mode. + + Any field of an envelope or address which is + not applicable is presented as the atom NIL. + Note that the server must default the reply-to + and sender fields from the from field; a client is + not expected to know to do this. + + FLAGS An S-expression format list of flags which are set + for this message. This may include the following + system flags: + + \RECENT Message arrived since last + read of this mailbox + \SEEN Message has been read + \ANSWERED Message has been answered + \FLAGGED Message is "flagged" for + urgent/special attention + \DELETED Message is "deleted" for + removal by later EXPUNGE + + INTERNALDATE A string containing the date and time the + message was written to the mailbox. + + RFC822 A string expressing the message in RFC 822 + format. + Note: Some implementations of IMAP2 servers + had the (undocumented) behavior of setting + the \SEEN flag as a side effect of fetching + the body of a message. This resulted in + erroneous behavior for clients that prefetch + messages that the user might not get + around to reading. Thus, this behavior is + explicitly disallowed in IMAP3. + Note: this is not a significant performance + restriction because it is always possible for + IMAP3 clients to use an interaction with the + server of the following type: + A001 FETCH 42 RFC822 + A002 STORE 42 +FLAGS (\SEEN) + A001 42 FETCH RFC822 {637} ...... + A001 OK Fetch completed + A002 42 STORE FLAGS (\SEEN \FLAGGED...) + A002 OK Store Completed. + + RFC822.HEADER A string expressing the RFC 822 format + header of the message + + + + +Rice [Page 29] + +RFC 1203 IMAP3 February 1991 + + + RFC822.SIZE A number indicating the number of + characters in the message as expressed + in RFC 822 format. + + RFC822.TEXT A string expressing the text body of the + message, omitting the RFC 822 header. + See also note for RFC822. + + */tag FLAGS flag_list + + A solicited FLAGS response must occur as a result of a SELECT + command. The flag list is the list of flags (at a minimum, the + IMAP defined flags) which are applicable for this mailbox. Flags + other than the system flags are a function of the server + implementation. + + */tag SEARCH (numbers) (search_criteria) + + This response occurs as a result of a SEARCH command. The + number(s) refer to those messages which match the search criteria. + In its solicited form this message allows clients to find + interesting groups of messages, e.g., unseen messages from + Crispin. In its unsolicited form it allows the server to inform + the client of interesting patterns, e.g., when new mail arrives, + recent and from Crispin. Compatibility note: The search_criteria + are sent by the server along with the matching numbers so + unsolicited SEARCH messages may be interpreted. This syntax is + not upwards compatible with IMAP2 and so the new syntax is + intended to make it simple for clients that are not able to take + advantage of unsolicited SEARCH messages still to interpret + solicited SEARCH messages simply by ignoring everything that + follows the list of numbers with minimal parsing. Such clients + may not, however, simply discard the rest of the line because + there might be LITERALs in the search pattern. + + Examples: + A00042 SEARCH (2 3 6) (FROM Crispin ~SEEN) + and + * SEARCH (42) (FROM Crispin RECENT) + + */tag READONLY + + This indicates that the mailbox is read-only. The server is + required to respond to a READONLY or READWRITE command with either + a solicited READONLY or a solicited READWRITE response. Note: If + the client attempts a mutation operation, such as STORE, on a + mailbox to which it does not have write access then the server is + required to reply with a solicited READONLY response on the first + + + +Rice [Page 30] + +RFC 1203 IMAP3 February 1991 + + + such attempted mutation. The server may also choose to send + solicited READONLY responses for each subsequent attempted + mutation. + + */tag READWRITE + + This indicates that the mailbox is read-write. The server is + required to respond to a READONLY or READWRITE command with either + a solicited READONLY or a solicited READWRITE response. + + */tag BBOARD bboard_name + + This message is produced in its solicited form as a response to a + FIND BBOARDS command. In its unsolicited form it represents a + notification by the server that a new BBoard has been added. + Bboard_name must be a name that can be supplied to the BBOARD + command so as to select the appropriate bboard. + + */tag MAILBOX non_inbox_mailbox_name + + This message is produced in its solicited form as a response to a + FIND MAILBOXES command. In its unsolicited form it represents a + notification by the server that a new mailbox has been added, + perhaps as the result of a COPY command creating a new mailbox. + Non_inbox_mailbox_name must be a name that can be supplied to the + SELECT command so as to select the appropriate mailbox. Note: + non_inbox_mailbox_name is never the string "INBOX". + + */tag SUPPORTED.VERSIONS (version_specs) + + This message is used either as a response to the + SUPPORTED.VERSIONS or, in its unsolicited form, to indicate the + dynamic addition or removal of support for features or protocol + versions. Each version_spec is of the form (4 2 + EIGHT.BIT.TRANSPARENT AUTO.SET.SEEN ...), i.e., a major version + number and a minor version number for the protocol and the set of + features supported under the server's implementation of that + protocol version. A server may not dynamically remove support for + any version or feature that has been selected by any currently + logged in client by the use of the VERSION command. + + Example: + A00005 SUPPORTED.VERSIONS ((2 0 ) + (2 2 TAGGED.SOLICITED) + (3 0 EIGHT.BIT.TRANSPARENT TAGGED.SOLICITED)) + + Indicates that two major versions are supported and one minor + version is supported and that tagged solicited messages are + + + +Rice [Page 31] + +RFC 1203 IMAP3 February 1991 + + + supported in versions 2.2 and 3.0 with eight bit characters being + supported under version 3. For each feature mentioned in the list + of features there is also always the negation of that feature. + For example, if the server supports the TAGGED.SOLICITED feature + then it also supports the ~TAGGED.SOLICITED feature, which + disables this feature. Note: These are only example feature + names and are not necessarily supported by any server. See the + appendix on features for more information on features. + + + text + + This response indicates that the server is ready to accept the + text of a literal from the client. Normally, a command from the + client is a single text line. If the server detects an error in + the command, it can simply discard the remainder of the line. It + cannot do this in the case of commands which contain literals, + since a literal can be an arbitrarily long amount of text, and the + server may not even be expecting a literal. This mechanism is + provided so the client knows not to send a literal until the + server definitely expects it, preserving client/server + synchronization. + + In actual practice, this situation is rarely encountered. In the + current protocol, the only client commands likely to contain + literals are the LOGIN command and the STORE RFC822.HEADER or + STORE RFC822.TEXT commands. Consider a situation in which a + server validates the user before checking the password. If the + password contains "funny" characters and hence is sent as a + literal, then if the user is invalid an error would occur before + the password is parsed. + + No such synchronization protection is provided for literals sent + from the server to the client, for performance reasons. Any + synchronization problems in this direction would be due to a bug + in the client or server and not for some operational problem. + +Sample IMAP3 session + + The following is a transcript of an actual IMAP3 session. Server + output is identified by "S:" and client output by "U:". In cases + where lines were too long to fit within the boundaries of this + document, the line was continued on the next line preceded by a tab. + + S: * OK SUMEX-AIM.Stanford.EDU Interactive Mail Access Protocol + III Service 6.1(349) at Mon, 14 May 90 14:58:30 PDT + U: a001 SUPPORTED.VERSIONS + S: * SUPPORTED.VERSIONS ((2 0 ) (3 0 EIGHT.BIT.TRANSPARENT + AUTO.SET.SEEN TAGGED.SOLICITED)) + + + +Rice [Page 32] + +RFC 1203 IMAP3 February 1991 + + + S: A001 Supported Versions returned. + U: a002 SELECT.VERSION (3 0) + S: a002 OK Version 3.0 Selected. + U: a003 SELECT.FEATURES TAGGED.SOLICITED + S: a003 OK Features selected. + U: a004 login crispin secret + S: a004 OK User CRISPIN logged in at Thu, 9 Jun 90 14:58:42 PDT, + job 76 + U: a005 select inbox + S: a005 FLAGS (Bugs SF Party Skating Meeting Flames Request AI + Question Note \XXXX \YYYY \Answered \Flagged \Deleted + \Seen) + S: a005 16 EXISTS + S: a005 0 RECENT + S: a006 OK Select complete + U: a006 fetch 16 all + S: a006 16 Fetch (Flags (\Seen) InternalDate " 9-Jun-88 12:55: + RFC822.Size 637 Envelope ("Sat, 4 Jun 88 13:27:11 PDT" + "INFO-MAC Mail Message" (("Larry Fagan" NIL "FAGAN" + "SUMEX-AIM.Stanford.EDU" NIL)) (("Larry Fagan" NIL "FAGAN" + "SUMEX-AIM.Stanford.EDU" NIL)) (("Larry Fagan" NIL "FAGAN" + "SUMEX-AIM.Stanford.EDU" NIL)) ((NIL NIL "rindflEISCH" + "SUMEX-AIM.Stanford.EDU" NIL)) NIL NIL NIL + "<12403828905.13.FAGAN@SUMEX-AIM.Stanford.EDU>")) + S: a006 OK Fetch completed + U: a007 fetch 16 rfc822 + S: a007 16 Fetch (RFC822 {637} + S: Mail-From: RINDFLEISCH created at 9-Jun-88 12:55:43 + S: Mail-From: FAGAN created at 4-Jun-88 13:27:12 + S: Date: Sat, 4 Jun 88 13:27:11 PDT + S: From: Larry Fagan <FAGAN@SUMEX-AIM.Stanford.EDU> + S: To: rindflEISCH@SUMEX-AIM.Stanford.EDU + S: Subject: INFO-MAC Mail Message + S: Message-ID: <12403828905.13.FAGAN@SUMEX-AIM.Stanford.EDU> + S: ReSent-Date: Thu, 9 Jun 88 12:55:43 PDT + S: ReSent-From: TC Rindfleisch <Rindfleisch@SUMEX-AIM.Stanford.EDU> + S: ReSent-To: Yeager@SUMEX-AIM.Stanford.EDU, + Crispin@SUMEX-AIM.Stanford.EDU + S: ReSent-Message-ID: + <12405133897.80.RINDFLEISCH@SUMEX-AIM.Stanford.EDU> + S: + S: The file is <info-mac>usenetv4-55.arc ... + S: Larry + S: ------- + S: ) + S: a007 OK Fetch completed + U: a008 logout + S: a008 BYE UNIX IMAP III server terminating connection + + + +Rice [Page 33] + +RFC 1203 IMAP3 February 1991 + + + S: a008 OK SUMEX-AIM.Stanford.EDU Interim Mail Access Protocol + Service logout + +Implementation Discussion + + As of this writing, SUMEX has completed an IMAP2 client for Xerox + Lisp machines written in hybrid Interlisp/CommonLisp and is beginning + distribution of a client for TI Explorer Lisp machines. SUMEX has + also completed a portable IMAP2 client protocol library module + written in C. This library, with the addition of a small main + program (primarily user interface) and a TCP/IP driver, became a + rudimentary remote system mail-reading program under Unix. The first + production use of this library is as a part of a MacII client which + has now been under daily use (by real users) at Stanford for quite + some time. + + As of this writing, SUMEX has completed IMAP2 servers for TOPS-20 + written in DEC-20 assembly language and 4.2/3 BSD Unix written in C. + The TOPS-20 server is fully compatible with MM-20, the standard + TOPS-20 mailsystem, and requires no special action or setup on the + part of the user. The INBOX under TOPS-20 is the user's MAIL.TXT. + The TOPS-20 server also supports multiple simultaneous access to the + same mailbox, including simultaneous access between the IMAP3 server + and MM-20. The 4.2/3 BSD Unix server requires that the user use + either Unix Mail format or mail.txt format which is compatible with + SRI MM-32 or Columbia MM-C. The 4.2/3 BSD Unix server allows + simultaneous read access; write access must be exclusive. There is + also an experimental IMAP3 server running on the TI Explorer class of + machine, which uses MM mailbox format and which can communicate over + both TCP and Chaos. + + The Xerox Lisp client and DEC-20 server have been in production use + for over two years; the Unix server was been in production use for + over a year. IMAP3 has been used to access mailboxes at remote sites + from a local workstation via the Internet. For example, from the + Stanford local network one of the authors has read his mailbox at a + Milnet site. + + A number of IMAP clients have now been developed or are being + developed. Amongst these are versions that run on the following + machines: + + . Xerox Lisp machines + . Apple Macintosh + . NeXT + . IBM PC + . TI Explorer Lisp machines + . "Glass teletype" version that runs under Unix + + + +Rice [Page 34] + +RFC 1203 IMAP3 February 1991 + + + . GNU Emacs + . X Windows + . NTT ELIS + + Each of these client programs is carefully tuned to optimize the + performance and user interface in a manner that is consistent with + the the user interface model of the native machine. For example, the + Macintosh client features a "messy-desk" interface that allows the + cutting and pasting of text with the use of the clipboard with a menu + driven interface with keyboard accelerators. + + This specification does not make any formal definition of size + restrictions, but some of the existing servers have the following + limitations: + + DEC-20 + . length of a mailbox: 7,077,888 characters + . maximum number of messages: 18,432 messages + . length of a command line: 10,000 characters + . length of the local host name: 64 characters + . length of a "short" argument: 39 characters + . length of a "long" argument: 491,520 characters + . maximum amount of data output in a single fetch: + 655,360 characters + + TI-Explorer + . length of a mailbox: limited by the Minimum of the size of the + virtual address space and the size of the file system + . maximum number of messages: limited by the the size of the + virtual address space + . length of a command line: limited by the the size of the + virtual address space + . length of the local host name: limited by the the size of the + virtual address space + . length of a "short" argument: limited by the the size of the + virtual address space + . length of a "long" argument: limited by the the size of the + virtual address space + . maximum amount of data output in a single fetch: not limited + + Typical values for these limits are 30Mb for file systems and 128Mb + for virtual address space. + + To date, nobody has run up against any of these limitations, many of + which are substantially larger than most current user mail reading + programs. + + There are several advantages to the scheme of tags and solicited + + + +Rice [Page 35] + +RFC 1203 IMAP3 February 1991 + + + responses and unsolicited data. First, the infamous synchronization + problems of SMTP and similar protocols do not happen with tagged + commands; a command is not considered satisfied until a completion + acknowledgement with the same tag is seen. Tagging allows an + arbitrary amount of other responses ("solicited" data) to be sent by + the server with no possibility of the client losing synchronization. + Compare this with the problems that FTP or SMTP clients have with + continuation, partial completion, and commentary reply codes. + + Another advantage is that a non-lockstep client implementation is + possible. The client could send a command, and entrust the handling + of the server responses to a different process which would signal the + client when the tagged response comes in. Some clients might be + implemented in a thoroughly asynchronous manner, having, perhaps, + multiple outstanding commands at any given time. Note: this does + not require that the server process these commands in anything other + than a lock-step manner. It simply allows clients to take advantage + of servers that are able to do such asynchronous operations. + + It was observed that synchronization problems can occur with literals + if the literal is not recognized as such. Fortunately, the cases in + which this can happen are relatively rare; a mechanism (the special + "+" tag response) was introduced to handle those few cases which + could happen. The proper way to address this problem in all cases is + probably to move towards a record-oriented architecture instead of + the text stream model provided by TCP. + + Unsolicited data needs some discussion. Unlike most protocols, in + which the server merely does the client's bidding, an IMAP3 server + has a semi-autonomous role. By means of sending "unsolicited data", + the server is in effect sending a command to the client -- to update + and/or extend its (incomplete) model of the mailbox with new + information from the server. In this viewpoint, although a "fetch" + command is a request for specific information from the client, the + server is always at liberty to include more than the desired data as + "unsolicited". A server acknowledgement to the "fetch" is a + statement that at least all the requested data has been sent. + + In terms of implementation, a simple lock-step client may have a + local cache of data from the mailbox. This cache is incomplete in + general, and at select time is empty. A listener on the IMAP + connection in the client processes all solicited and unsolicited data + symmetrically, and updates the cache based on this data, i.e., the + client faults on a cache miss and asks the server to fill that cache + slot synchronously. If a tagged completion response arrives, the + listener unblocks the process which sent the tagged request. + + Clearly, given this model it is not strictly necessary to distinguish + + + +Rice [Page 36] + +RFC 1203 IMAP3 February 1991 + + + most solicited from unsolicited data. Doing so, however, apart from + being clearer, also allows such simplistic, lock-step client + implementations that extract the specific value of the response to + command by trapping the tagged response. This allows the client not + to have to block on some complex predicate that involves watching to + see an update in a cache cell. + + For example, perhaps as a result of opening a mailbox, solicited data + from the server arrives. The first piece of data is the number of + messages. This is used to size the cache; note that, if new mail + arrives, by sending a new "number of messages" unsolicited data + message server will cause the cache to be re-sized. If the client + attempts to access information from the cache, it will encounter + empty spots which will trigger "fetch" requests. The request would + be sent, some solicited data including the answer to the fetch will + flow back, and then the "fetch" response will unblock the client. + + People familiar with demand-paged virtual memory design will + recognize this model as being very similar to page-fault handling on + a demand-paged system. + +Formal Syntax + + The following syntax specification uses the augmented Backus-Naur + Form (BNF) notation as specified in RFC 822 with one exception; the + delimiter used with the "#" construct is a single space (SP) and not + a comma. + +address ::= "(" addr_name SP addr_adl SP addr_mailbox SP + addr_host addr_comment ")" + +addr_adl ::= nil / string + +addr_comment ::= nil / string + +addr_host ::= nil / string + +addr_mailbox ::= nil / string + +addr_name ::= nil / string + +bboard ::= "BBOARD" SP bboard_name + +bboard_name ::= string + +bboard_notify ::= "BBOARD" sp bboard_name + +canonical_key ::= "$CC" / "$FROM" / "$SUBJECT" / "$TO" + + + +Rice [Page 37] + +RFC 1203 IMAP3 February 1991 + + +check ::= "CHECK" + +concrete_key ::= string + +copy ::= "COPY" SP sequence SP mailbox + +criterion ::= "ALL" / "ANSWERED" / + "BCC" SP string / "BEFORE" SP string / + "BODY" SP string / "CC" SP string / "DELETED" / + "FLAGGED" / "KEYWORD" SP atom / "NEW" / "OLD" / + "ON" SP string / "RECENT" / "SEEN" / + "SINCE" SP string / "TEXT" SP string / + "TO" SP string / "UNANSWERED" / "UNDELETED" / + "UNFLAGGED" / "UNKEYWORD" / "UNSEEN" / key SP string + +criteria ::= 1#criterion + +data ::= ("FLAGS" SP flag_list / + search_notify / bboard_notify / mailbox_notify / + supported_versions_notify / "READONLY" / "READWRITE" / + "BYE" SP text_line / "OK" SP text_line / + "NO" SP text_line / "BAD" SP text_line) + +date ::= string in form "dd-mmm-yy hh:mm:ss-zzz" + +envelope ::= "(" env_date SP env_subject SP env_from SP + env_sender SP env_reply-to SP env_to SP + env_cc SP env_bcc SP env_in-reply-to SP + env_message-id ")" + +env_bcc ::= nil / "(" 1*address ")" + +env_cc ::= nil / "(" 1*address ")" + +env_date ::= string + +env_from ::= nil / "(" 1*address ")" + +env_in-reply-to ::= nil / string + +env_length ::= NUMBER + +env_message-id ::= nil / string + +env_reply-to ::= nil / "(" 1*address ")" + +env_sender ::= nil / "(" 1*address ")" + + + + +Rice [Page 38] + +RFC 1203 IMAP3 February 1991 + + +env_subject ::= nil / string + +env_to ::= nil / "(" 1*address ")" + +expunge ::= "EXPUNGE" + +feature ::= ATOM + +fetch ::= "FETCH" SP sequence SP ("ALL" / "FAST" / + fetch_att / "(" 1#fetch_att ")") + +fetch_att ::= "ENVELOPE" / "FLAGS" / "INTERNALDATE" / + "RFC822" / "RFC822.HEADER" / "RFC822.SIZE" / + "RFC822.TEXT" / key + +find ::= "FIND" ("BBOARDS" / "MAILBOXES") pattern + +flag_list ::= ATOM / "(" 1#ATOM ")" + +flags ::= "FLAGS" + +generic_key ::= "BCC" / "BODY" / "CC" / "FROM" / "HEADER" / "SIZE" / + "SUBJECT" / "TEXT" / "TO" + +key ::= generic_key / canonical_key / concrete_key + +literal ::= "{" NUMBER "}" CRLF ASCII-STRING + +login ::= "LOGIN" SP userid SP password + +logout ::= "LOGOUT" + +mailbox ::= "INBOX" / string + +mailbox_notify ::= MAILBOX non_inbox_mailbox_name + +msg_copy ::= "COPY" + +msg_data ::= (msg_exists / msg_recent / msg_expunge / + msg_fetch / msg_copy) + +msg_exists ::= "EXISTS" + +msg_expunge ::= "EXPUNGE" + +msg_fetch ::= ("FETCH" / "STORE") SP "(" 1#("ENVELOPE" SP + env_length envelope / "FLAGS" SP "(" 1#(recent_flag + flag_list) ")" / "INTERNALDATE" SP date / + + + +Rice [Page 39] + +RFC 1203 IMAP3 February 1991 + + + "RFC822" SP string / "RFC822.HEADER" SP string / + "RFC822.SIZE" SP NUMBER / "RFC822.TEXT" SP + string / key SP string_list) ")" + +msg_recent ::= "RECENT" + +msg_num ::= NUMBER + +nil ::= "NIL" + +non_inbox_mailbox_name ::= string + +noop ::= "NOOP" + +numbers ::= 1#NUMBER + +password ::= string + +pattern ::= string + +recent_flag ::= "\RECENT" + +read_only ::= "READONLY" + +read_write ::= "READWRITE" + +ready ::= "+" SP text_line + +request ::= tag SP (noop / login / logout / select / check / + expunge / copy / fetch / store / search / + select_version / select_features / + supported_versions / bboard / find / + read_only / read_write / flags / set_flags ) CRLF + +response ::= tag SP ("OK" / "NO" / "BAD") SP text_line CRLF + +search ::= "SEARCH" SP criteria + +search_notify ::= "SEARCH" SP (numbers) SP (criteria) + +select ::= "SELECT" SP mailbox + +select_features ::= "SELECT.FEATURES" 1#feature + +select_version ::= "SELECT.VERSION" SP "(" NUMBER SP NUMBER ")" + +sequence ::= NUMBER / (NUMBER "," sequence) / (NUMBER ":" + sequence) + + + +Rice [Page 40] + +RFC 1203 IMAP3 February 1991 + + +set_flags ::= "SET.FLAGS" SP flag_list + +solicited ::= tag SP (msg_num SP msg_data / data / + solicited_only) CRLF + +solicited_only ::= {None currently defined} + +store ::= "STORE" SP sequence SP store_att + +store_att ::= ("+FLAGS" SP flag_list / "-FLAGS" SP flag_list / + "FLAGS" SP flag_list / RFC822.TEXT SP string + / RFC822.HEADER SP string / key SP string) + +string ::= atom / """" 1*character """" / literal + +string_list ::= string / ("(" 1#string ")") + +supported_versions ::= "SUPPORTED.VERSIONS" + +supported_versions_notify ::= "SUPPORTED.VERSIONS" "(" 1#version_spec + ")" + +system_flags ::= "\ANSWERED" SP "\FLAGGED" SP "\DELETED" SP + "\SEEN" + +tag ::= atom + +unsolicited ::= "*" SP (msg_num SP msg_data / data) CRLF + +userid ::= string + +version_spec ::= "(" NUMBER SP NUMBER SP 1#feature ")" + +Appendix: Features. + + In this section we outline the standard features that are supported + by all IMAP3 servers and identify those features which are + recommended or experimental. For each of these features the default + setting is specified. This means that it is required of any server + that supports a given feature to make the default enabledness of that + feature as is specified below. It is required that for each feature + supported by a server the inverse feature should also be supported. + The inverse feature name shall always be defined as the feature name + preceded by the "~" character. Thus, the AUTO.SET.SEEN feature is + disabled by the ~AUTO.SET.SEEN feature. + + + + + + +Rice [Page 41] + +RFC 1203 IMAP3 February 1991 + + + Required Features: + + AUTO.SET.SEEN - When this features is enabled (default is disabled), + the \\SEEN flag is set for all appropriate messages as a side + effect of any of the following: + FETCH of RFC822 + FETCH of RFC822.TEXT + COPY + Justification: This feature is provided for the use of clients + that are unable to pipeline their commands effectively and + communicate over high latency connections. When disabled, + the server will not perform any such side effects. This feature + is also provided so as to smooth the transition from IMAP2 to + IMAP3. + + + TAGGED.SOLICITED - When this feature is enabled (default is enabled + for IMAP3, disabled for IMAP2 mode), solicited responses from + the server will have the tag specified by the client. + When this feature is disabled, solicited responses from the + server will have the IMAP2 compatible tag "*", not the + tag specified by the client. + Justification: This feature is provided so as to smooth the + transition from IMAP2 to IMAP3. + + Recommended Features. + + EIGHT.BIT.TRANSPARENT - When this feature is enabled + (default is disabled), the server allows the transparent + transmission of eight bit characters. When this feature is + disabled, the value of any bit other than the least significant + 7 bits transmitted by the server is unspecified. If this + feature is enabled, the characters that compose all command + keywords specified in the IMAP3 grammar and all feature names + use only their 7 least significant bits. + Justification: This feature is provided for the purpose of + supporting national character sets within messages, encoded + languages such as Japanese Kanji characters and also of binary + data, such as programs, graphics and sound. + + + NEW.MAIL.NOTIFY - When this feature is enabled (default is + disabled for compatibility with the majority of existing + IMAP2 servers), the server will notify the client of the + arrival of new mail in the currently selected mailbox + using the appropriate RECENT and EXISTS unsolicited messages + without the client needing to send periodic CHECK commands. + Justification: This feature is provided to allow clients to + + + +Rice [Page 42] + +RFC 1203 IMAP3 February 1991 + + + switch off any periodic polling strategy that they may use + to look for new mail. Such polling unnecessarily uses bandwidth + and can cause the interactive performance to degrade because + the user can be kept waiting while some background process + is doing a CHECK. + + + SEND - When this feature is enabled (default is disabled) a new + "SEND" command becomes available to the client. The SEND + command instructs the server to send a message, rather + than requiring the client to use its own, local message + sending capability, for example. An example of of the + send command might be as follows: + tag42 SEND RFC822 {2083} + From: James Rice <Rice@Sumex-Aim.Stanford.Edu> + To:..... + If the server is unable to parse the message being sent then + it is required to issue a suitable NO notification to the client. + If the message cannot be delivered for some reason then the + server should send a suitable message to the FROM: address + of the message detailing the delivery failure. + When the SEND feature is enabled, the "send" production in + the grammar is added and as defined below. The "send" + request is added to the list of requests in the request + production also as shown below: + + message_format ::= RFC822 + + request ::= tag SP (noop / login / logout / select / check / + expunge / copy / fetch / store / search / + select_version / select_features / + supported_versions / bboard / find / + read_only / read_write / flags / + set_flags / send) CRLF + + send ::= SEND SP message_format SP string + + Justification: This feature is provided so that mail can be + sent by the same reliable server that is used for the storage + of mail. This has, amongst others, the following benefits: + - Single process clients need not be delayed by mail + transmission. + - Mail sent by the client will have the server named as the + message's sender. This can be important because there are + a lot of mailers that erroneously cause reply mail to be + sent to the Sender, not the From or Reply-To address. Since + the client in general is not listening for mail being sent + to it directly this can cause mail to be lost. + + + +Rice [Page 43] + +RFC 1203 IMAP3 February 1991 + + + - Clients can be written that do not have any native message + sending capability. + + + ADD.MESSAGE - When this feature is enabled (default is disabled) + a new "ADD.MESSAGE" command becomes available to the client. + The ADD.MESSAGE command instructs the server to add the + specified message to the designated mailbox. This command + can be thought of as being like a COPY command except in + this case the message that is put in the designated mailbox + is specified as a string, rather than as a message number to + be copied from the currently selected mailbox. An example + use of this command might be as follows: + tag42 ADD.MESSAGE OUTGOING-MAIL RFC822 {2083} + From: James Rice <Rice@Sumex-Aim.Stanford.Edu> + To:..... + This will have the effect of adding the message to the mailbox + called OUTGOING-MAIL. + If the server is unable to parse the message being added then + it is required to issue a suitable NO notification to the client. + When the ADD.MESSAGE feature is enabled, the "add_message" + production in the grammar is added and as defined below. + The "add_message" request is added to the list of requests + in the request production also as shown below: + + add_message ::= ADD.MESSAGE SP mailbox SP format SP string + + message_format ::= RFC822 + + request ::= tag SP (noop / login / logout / select / check / + expunge / copy / fetch / store / search / + select_version / select_features / + supported_versions / bboard / find / + read_only / read_write / flags / set_flags / + add_message) CRLF + + Justification: This feature is provided so that clients can + easily add mail to specific mailboxes. This allows clients + to implement such behavior as outgoing mail storage (BCC) + without the need to resort to mailing to special BCC mailboxes. + + + RENUMBER - When this feature is enabled (default is disabled) + the RENUMBER command becomes available to the client. + The RENUMBER command will reorder the assignment of message + numbers to the messages in the mailbox. If this results in a + change to the association of any message number with any + message then the server is required to send solicited RESET + + + +Rice [Page 44] + +RFC 1203 IMAP3 February 1991 + + + responses to the client. The intent of this command is + to allow users to view mailboxes in user-meaningful order + efficiently. While the client could do the ordering, + it would be less efficient in general. Note that the + server may or may not change the actual storage of the + messages and the ordering may or may not remain in effect + after another mailbox is selected or the IMAP session is + terminated. Informally, the syntax for the RENUMBER + command is: + + tag RENUMBER field_name ordering_type + + this has the effect of changing the IMAP grammar to be + as follows: + + ordering_type ::= DATE / NUMERIC / ALPHA + + renumber ::= RENUMBER SP field_name SP ordering_type + + request ::= tag SP (noop / login / logout / select / check / + expunge / copy / fetch / store / search / + select_version / select_features / + supported_versions / bboard / find / + read_only / read_write / flags / set_flags / + renumber) CRLF + + For example: + tag42 RENUMBER FROM ALPHA + ;;;RENUMBER alphabetically by the from field + tag42 RESET 10:20,49 + ;;;Messages 10 to 20 and 49 have changed + tag42 OK RENUMBER finished. Sequence has changed + tag43 FETCH ALL 10:20,49 + ;;;Client chooses to fetch the changed msgs. + + To support this the RESET message is defined as follows: + + */tag RESET message_sequence + This solicited of unsolicited message from the server informs the + client that it should flush any information that it has + retained for the specified messages. + + Justification: This feature is provided so that clients can + view mailboxes in an order that is convenient to the user. + This is particularly important in the context of mailboxes + that the user copies messages to from other mailboxes. This + user-controlled filing process often does not happen in any + well-defined order. Because messages in a mailbox are + + + +Rice [Page 45] + +RFC 1203 IMAP3 February 1991 + + + implicitly ordered (usually by arrival date, though this is + not a required ordering predicate), the user can be confused + by the apparent order of messages in the mailbox. The + addition of the RENUMBER command makes it unnecessary + for the user to leave IMAP and use some other mail system to + sort mailboxes. + + + ENCODING - When this feature is enabled (default is disabled) a new + generic key named ENCODING is defined. The value associated + with the generic ENCODING key is a list of (tag encoding-type + options...) lists that represent the ordered, possibly encoded + body of the message. Each such list represents a segment of + the body of the message and the way in which it is encoded. + Any options that follow the encoding_type are further + qualifiers that describe the format of the segment. Each tag + is created by the server and is unique with respect to the + other tags allocated for the other elements in the ENCODING + list. The client may use the tags returned by the server as + concrete keys to access a field which is encoded using the + encoding type and options mentioned in the appropriate list. + Thus: + + tag41 FETCH 196 ENCODING ; Client asks for encoding field of msg 196. + tag41 FETCH ENCODING NIL ; Server replies. This message is not encoded. + tag41 OK Fetch completed. + tag42 FETCH 197 ENCODING ; Client asks for encoding field of msg 197. + tag42 FETCH ENCODING ((G001 UUENCODE) (G002 HEX)) ; Server replies. + tag42 OK Fetch completed. + tag43 FETCH 197 G002 ; Client asks for field named G002 + tag43 FETCH G002 "A0 00 FF 13 42......." ; Server sends value of field. + tag43 OK Fetch completed. + + or + + tag44 STORE 197 G002 "0A 00 FF 31 24......." + ; Store back the segment with nibbles swapped + + Note: As a side-effect of enabling this feature, the generic key + TEXT will be redefined so as to return only those body parts of a + message that are of type TEXT. The concrete key RFC822.TEXT, on + the other hand, would still return everything in the body of the + message, even if it was full of strange, binary character + sequences. + + When the client STOREs to a field denoted by one of the above tags + the server will interpret the value being passed as being in the + same format as is currently specified in the ENCODING field. The + + + +Rice [Page 46] + +RFC 1203 IMAP3 February 1991 + + + server is not required to be able to reformat the data associated + with the ENCODING tags if the client STOREs a new value for the + ENCODING field. The interpretability of a message in the context + of its ENCODING field is undefined if the client side-effects that + ENCODING field, unless the client also STOREs new, reformatted + values for the fields that have had their encoding changed. + + If the client stores a new value for the ENCODING field then the + tags in the new value will be used to index the parts of the body. + All tags in a client-STOREd ENCODING that are the same as those + originally generated by the server in response to a FETCH ENCODING + command are said still to denote the fields that they originally + denoted, though possibly reordered. Any tags not originally + defined by the server will denote new message parts, in the + appropriate format, in the relative position specified. The + exclusion of any tags that the server originally defined in a + FETCH of the ENCODING field will indicate the deletion of that + part of the message. Newly created message parts are undefined by + default, so if the client fails to follow the STOREing of the + ENCODING field with suitable STORE commands for the values + associated with any newly created tags, these fields will contain + the null value NIL. + + Justification: This feature is supplied so as to allow support + for emergent multi-part and multi-media mail standards. + + INDEXABLE.FIELDS - When this feature is enabled (default is + disabled) the grammar of fetch commands is changed to allow the + client to select a specific subsequence from the field in + question. For example: + + tag42 FETCH 197 BODY 2000:3999 + + would fetch the second two thousand bytes of the body of message + 197. This feature allows resource limited clients to access + small parts of large messages. The formal syntax for this is: + + fetch_att ::= "ENVELOPE" / "FLAGS" / "INTERNALDATE" / + fetch_key / (fetch_key SP NUMBER ":" NUMBER) + + fetch_key ::= "RFC822" / "RFC822.HEADER" / "RFC822.SIZE" / + "RFC822.TEXT" / key + + If the lower bound number (the number to the left of the colon) + exceeds the maximum size of the field then the empty string is + returned. If the upper bound exceeds the maximum size of the + field but the lower bound does not then the server will return the + remaining substring of the field after the lower bound. The + + + +Rice [Page 47] + +RFC 1203 IMAP3 February 1991 + + + bounds specified are zero indexed into the fields and the bounds + index fields by 8-bit bytes. + + Justification: This feature is provided so as to allow resource- + limited clients to read very large messages and also to allow + clients to improve interactive response for the reading of large + messages by fetching the first "screen full" of data to display + immediately and fetching the rest of the message in the + background. + + SET.EOL - When enabled (default is disabled), this feature + allows the new command SET.EOL to be available, changing the + grammar as follows: + + character ::= "CR" / "LF" / number + + request ::= tag SP (noop / login / logout / select / check / + expunge / copy / fetch / store / search / + select_version / select_features / + supported_versions / bboard / find / + read_only / read_write / flags / set_flags / + set_eol) CRLF + + set_eol ::= "SET.EOL" 1#character + + This has the effect of changing the end of line character sequence + generated by the server for newlines within strings to the + sequence of characters specified. The characters in the sequence + can be either the specified symbolically named characters or a + numerical value, specifying the decimal value of the character to + use. Thus, if the client would like newlines in strings to be + indicated by a carriage return followed by a control-d, the client + would issue the following command: + + tag42 SET.EOL CR 4 + + If the server is unable to support the combination of characters + requested by the client as its end-of-line pattern it will reply + with a NO response. This might be the case, for example, if a + server is only able to generate its own native line feed pattern + and the CRLF required by IMAP by default. + + The server is required to change any length denoting values, such + as envelope byte counts for all future transactions to reflect the + new eol setting. This change in reported sizes should apply to + all generic size fetching keys, but not to concrete ones such as + RFC822.SIZE, which by their very nature require a size measurement + in RFC822 format, i.e., with CRLF as the end-of-line convention. + + + +Rice [Page 48] + +RFC 1203 IMAP3 February 1991 + + + Justification: This feature is provided because frequently clients + and servers might have end-of-line conventions other than the CRLF + specified by RFC822. It is undesirable that the IMAP be linked + too closely to RFC822 and selecting a different convention might + allow substantial performance improvements in both clients and + servers by saving either client, server or both from having to + shuffle text around so as to add or remove non-local end-of-line + sequences. + +Acknowledgements: + + This text is based on RFC 1064 by Mark Crispin. + + The following have made major contributions to this proposed update + to the IMAP2 protocol: + + James Rice <Rice@sumex-aim.stanford.edu> + Richard Acuff <acuff@sumex-aim.stanford.edu> + Bill Yeager <yeager@sumex-aim.stanford.edu> + Christopher Lane <lane@sumex-aim.stanford.edu> + Bjorn Victor <Bjorn.Victor@docs.uu.se> + + Additional input was also received from: + + Andrew Sweer <sweer@sumex-aim.stanford.edu> + Tom Gruber <Gruber@sumex-aim.stanford.edu> + Kevin Brock <Brock@Sumex-Aim.Stanford.Edu> + Mark Crispin <MRC@cac.washington.edu> + +Security Considerations + + Security issues are not discussed in this memo. + +Author's Address + + James Rice + Stanford University + Knowledge Systems Laboratory + 701 Welch Road + Building C + Palo Alto, CA 94304 + + Phone: (415) 723-8405 + EMail: RICE@SUMEX-AIM.STANFORD.EDU + + + + + + + +Rice [Page 49] +
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