Remove RFCs from the trunk, since we don't distribute them anyways. All of the removed RFCs are listed in the design-notes.html file, with the exception of NNTP (RFC977). Also add a link to the "LAN Mail Protocols" document to the design-notes.html file.

svn path=/trunk/; revision=4013

1 files changed, 0 insertions, 1392 deletions

diff --git a/RFC/rfc937.txt b/RFC/rfc937.txt
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--- a/RFC/rfc937.txt
+++ /dev/null
@@ -1,1392 +0,0 @@
-
-
-Network Working Group                                          M. Butler
-Request for Comments: 937                                      J. Postel
-                                                                D. Chase
-                                                           J. Goldberger
-                                                          J. K. Reynolds
-Obsoletes: RFC 918                                                   ISI
-                                                           February 1985
-
-
-                    POST OFFICE PROTOCOL - VERSION 2
-
-
-Status of this Memo
-
-   This RFC suggests a simple method for workstations to dynamically
-   access mail from a mailbox server.  This RFC specifies a proposed
-   protocol for the ARPA-Internet community, and requests discussion and
-   suggestions for improvement.  This memo is a revision of RFC 918.
-   Distribution of this memo is unlimited.
-
-Introduction
-
-   The intent of the Post Office Protocol Version 2 (POP2) is to allow a
-   user's workstation to access mail from a mailbox server.  It is
-   expected that mail will be posted from the workstation to the mailbox
-   server via the Simple Mail Transfer Protocol (SMTP).  For further
-   information see RFC-821 [1] and RFC-822 [2].
-
-   This protocol assumes a reliable data stream such as provided by TCP
-   or any similar protocol.  When TCP is used, the POP2 server listens
-   on port 109 [4].
-
-System Model and Philosophy
-
-   While we view the workstation as an Internet host in the sense that
-   it implements IP, we do not expect the workstation to contain the
-   user's mailbox.  We expect the mailbox to be on a server machine.
-
-   We believe it is important for the mailbox to be on an "always up"
-   machine and that a workstation may be frequently powered down, or
-   otherwise unavailable as an SMTP server.
-
-   POP2 is designed for an environment of workstations and servers on a
-   low-delay, high-throughput, local networks (such as Ethernets).  POP2
-   may be useful in other environments as well, but if the environment
-   is substantially different, a different division of labor between the
-   client and server may be appropriate, and a different protocol
-   required.
-
-   Suppose the user's real name is John Smith, the user's machine is
-   called FIDO, and that the mailbox server is called DOG-HOUSE.  Then
-
-
-
-Butler, et. al.                                                 [Page 1]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-   we expect the user's mail to be addressed to JSmith@DOG-HOUSE.ARPA
-   (not JSmith@FIDO.ARPA).
-
-   That is, the destination of the mail is the mailbox on the server
-   machine.  The POP2 protocol and the workstation are merely a
-   mechanism for viewing the messages in the mailbox.
-
-   The user is not tied to any particular workstation for accessing his
-   mail.  The workstation does not appear as any part of the mailbox
-   address.
-
-   This is a very simple protocol.  This is not a user interface.  We
-   expect that there is a program in the workstation that is friendly to
-   the user.  This protocol is not "user friendly".  One basic rule of
-   this protocol is "if anything goes wrong close the connection".
-   Another basic rule is to have few options.
-
-   POP2 does not parse messages in any way.  It does not analyze message
-   headers (Date:, From:, To:, Cc:, or Subject:).  POP2 simply transmits
-   whole messages from a mailbox server to a client workstation.
-
-The Protocol
-
-   The POP2 protocol is a sequence of commands and replies.  The design
-   draws from many previous protocols of the ARPA-Internet community.
-
-      The server must be listening for a connection.  When a connection
-      is opened the server sends a greeting message and waits for
-      commands.  When commands are received the server acts on them and
-      responds with replies.
-
-      The client opens a connection, waits for the greeting, then sends
-      the HELO command with the user name and password arguments to
-      establish authorization to access mailboxes.  The server returns
-      the number of messages in the default mailbox.
-
-      The client may read the default mailbox associated with the user
-      name or may select another mailbox by using the FOLD command.  The
-      server returns the number of messages in the mailbox selected.
-
-      The client begins a message reading transaction with a READ
-      command.  The read command may optionally indicate which message
-      number to read, the default is the current message (incremented
-      when a message is read and set to one when a new folder is
-      selected).  The server returns the number of characters in the
-      message.
-
-
-
-
-Butler, et. al.                                                 [Page 2]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-      The client asks for the content of the message to be sent with the
-      RETR command.  The server sends the message data.
-
-      When all the data has been received the client sends an
-      acknowledgment command.  This is one of ACKS, ACKD, and NACK.
-
-         ACKS means "I've received the message successfully and please
-         keep it in the mailbox".
-
-         ACKD means "I've received the message successfully and please
-         delete it from the mailbox".
-
-         NACK means "I did not receive the message and please keep it in
-         the mailbox".
-
-      In the case of ACKS or ACKD the server increments the current
-      message indicator.  In the case of NACK the current message
-      indicator stays the same.
-
-      In all cases the server returns the number of characters in the
-      (now) current message.
-
-      The client terminates the session with the QUIT command.  The
-      server returns an ok.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-Butler, et. al.                                                 [Page 3]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-   The Normal Scenario
-
-           Client                    Server
-           ------                    ------
-                                Wait for Connection
-      Open Connection  -->
-                           <--  + POP2 Server Ready
-                                Wait for Command
-      HELO Fred Secret -->
-                           <--  #13 messages for you
-                                Wait for Command
-      READ 13          -->   
-                           <--  =537 characters in that message
-                                Wait for Command
-      RETR             -->   
-                           <--  (send the message data)
-                                Wait for Command
-      ACKS             -->   
-                           <--  =0 no more messages
-                                Wait for Command
-      QUIT             -->
-                           <--  + OK
-      Close connection --> <--  Close connection
-                                Wait for Connection (go back to start)
-
-Conventions
-
-   Arguments
-
-      These arguments have system specific definitions.
-
-         user - A login account name.
-
-         password - The password for the login account.
-
-         mailbox - A mailbox name (also called a mail folder).
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-Butler, et. al.                                                 [Page 4]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-   Default Mailboxes
-
-      TOPS-20
-
-         MAIL.TXT.1 - from login directory
-
-      UNIX
-
-         both
-            /usr/spool/mail/user
-         and
-            /usr/user/Mail/inbox/*
-
-            where "user" is the user value supplied in the HELO command.
-
-   End of Line
-
-      End of Line is Carriage Return (CR) followed by Line Feed (LF).
-      This sequence is indicated by "CRLF" in this document.  This end
-      of line convention must be used for commands and replies.
-
-   Message Length
-
-      The reply to the READ command or an acknowledgment command (ACKS,
-      ACKD, NACK) is the length (a character count) of the next message
-      to be transmitted.  This includes all the characters in the data
-      transmitted.  CRLF counts as two characters.  A length of zero
-      means the message does not exist or is empty.  A request to
-      transmit a message of zero length will result in the server
-      closing the connection.  The message is transmitted in the
-      standard internet format described in RFC-822 [2] and NVT-ASCII.
-      This may be different from the storage format and may make
-      computing the message length from the stored message non-trivial.
-
-   Message Numbers
-
-      The reply to the HELO and FOLD commands is a count of the number
-      of messages in a the selected mailbox.  The READ command has a
-      message number as an optional argument.  These numbers are
-      decimal, start at one, and computed with respect to the current
-      mailbox.  That is, the first message in a mailbox is message
-      number 1.
-
-   Numbers
-
-      All numbers in this memo and protocol are decimal.
-
-
-
-
-Butler, et. al.                                                 [Page 5]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-   Quoting
-
-      In a few cases, there may be a need to have a special character in
-      an argument (user, password, or mailbox) that is not allowed by
-      the syntax.  For example, a space in a password. To allow for
-      this, a quoting convention is defined.  Unfortunately, such
-      quoting conventions "use up" another otherwise uninteresting
-      character.  In this protocol the back slash "\" is used as the
-      quote character.  To include a space in an argument the two
-      character sequence "back-slash, space" is transmitted.  To include
-      a back-slash in an argument the two character sequence
-      "back-slash, back-slash" is transmitted.  This quoting convention
-      is used in the command arguments only, it is not used in the mail
-      data transmitted in response to a RETR command.
-
-   Reply Strings
-
-      The first character is required to be as specified (i.e.,
-      "+", "-", "=", "#").  The optional strings that follow can be
-      whatever the implementer thinks is appropriate.
-
-Definitions of Commands and Replies
-
-   Summary of Commands and Replies
-
-      Commands                          Replies
-      --------                          -------
-      HELO user password                + OK
-      FOLD mailbox                      - Error
-      READ [n]                          #xxx
-      RETR                              =yyy
-      ACKS
-      ACKD
-      NACK
-      QUIT
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-Butler, et. al.                                                 [Page 6]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-   Commands
-
-      HELO user password
-
-         The Hello 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.  The
-         Hello command is the "HELO" keyword, followed by the user
-         argument, followed by the password argument, followed by CRLF.
-
-            Possible responses:
-
-               "#nnn"
-
-                  where nnn is the number of messages in the default
-                  mailbox,"
-
-               "- error report" and Close the connection.
-
-      FOLD mailbox
-
-         The Folder command selects another mailbox or mail folder.  The
-         server must check that the user is permitted read access to
-         this mailbox.  If the mailbox is empty or does not exist, the
-         number of messages reported is zero.  The Folder command is the
-         "FOLD" keyword, followed by the mailbox argument, followed by
-         CRLF.
-
-            Possible responses:
-
-               "#nnn"
-
-                  where nnn is the number of messages in this mailbox.
-
-      READ [nnn]
-
-         The Read command begins a message reading transaction.  If the
-         Read command is given without an argument the current message
-         is  implied (the current message indicator is incremented  by
-         the ACKS or ACKD commands).  If an argument is used with the
-         Read command it is the message number to be read, and this
-         command sets the current message indicator to that value.  The
-         server returns the count of characters in the message to be
-         transmitted.  If there is no message to be read, the count of
-         zero is returned.  If the message was previously deleted with
-         the ACKD command, the count of zero is returned.  The Read
-         command is followed by the RETR command, the READ command, the
-         FOLD command, or the QUIT command.  Do not attempt to RETR a
-
-
-Butler, et. al.                                                 [Page 7]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-         message of zero characters.  The Read command is the "READ"
-         keyword, optionally followed by the message number argument,
-         followed by CRLF.
-
-            Possible responses:
-
-               "=ccc"
-
-                  where ccc is the number of characters in this message.
-
-      RETR
-
-         The Retrieve command confirms that the client is ready to
-         receive the mail data.  It must be followed by an
-         acknowledgment command.  The server will close the connection
-         if asked to transmit a message of zero characters (i.e.,
-         transmit a non-existent message).  The message is transmitted
-         according to the Internet mail format standard RFC-822 [2] in
-         NVT-ASCII.  The Retrieve command is the "RETR" keyword,
-         followed by CRLF.
-
-            Possible responses:
-
-               the message data
-
-               Close the connection
-
-      ACKS
-
-         The Acknowledge and Save command confirms that the client has
-         received and accepted the message.  The ACKS command ends the
-         message reading transaction.  The message is kept in the
-         mailbox.  The current message indicator is incremented.  The
-         server returns the count of characters in the now current
-         message to be transmitted.  If there is no message to be read
-         or the message is marked deleted, the count of zero is
-         returned.  The Acknowledge and Save command is the "ACKS"
-         keyword, followed by CRLF.
-
-            Possible responses:
-
-               "=ccc"
-
-                  where ccc is the number of characters in the next
-                  message.
-
-
-
-
-
-Butler, et. al.                                                 [Page 8]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-      ACKD
-
-         The Acknowledge and Delete command confirms that the client has
-         received and accepted the message.  The ACKD command ends the
-         message reading transaction.  If the user is authorized to have
-         write access to the mailbox, the message is deleted from the
-         mailbox.  Actually, the message is only marked for deletion.
-         The actual change is made  when the mailbox is released at the
-         end of the session or when the client selects another mailbox
-         with the FOLD command.  The messages are not renumbered until
-         the mailbox is released.  If the user does not have write
-         access to the mailbox no change is made to the mailbox.  The
-         response is the same whether or not the message was actually
-         deleted.  The current message indicator is incremented.  The
-         server returns the count of characters in the now current
-         message to be transmitted.  If there is no message to be read
-         or the message is marked deleted, the count of zero is
-         returned.  The Acknowledge and Delete command is the "ACKD"
-         keyword, followed by CRLF.
-
-            Possible responses:
-
-               "=ccc"
-
-                  where ccc is the number of characters in the next
-                  message.
-
-      NACK
-
-         The Negative Acknowledge command reports that the client did
-         not receive the message.  The NACK command ends the message
-         reading transaction.  The message is kept in the mailbox.  The
-         current message indicator remains the same.  The server returns
-         the count of characters in the current message.  Since the
-         count to be returned is for the message just transmitted it the
-         message must exist and not be marked deleted, and the count
-         must be positive (non-zero).  The Negative Acknowledge command
-         is the "NACK" keyword, followed by CRLF.
-
-            Possible responses:
-
-               "=ccc"
-
-                  where ccc is the number of characters in this message.
-
-
-
-
-
-
-Butler, et. al.                                                 [Page 9]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-      QUIT
-
-         The Quit command indicates the client is done with the session.
-         The server sends an OK response and then closes the connection.
-         The Quit command is the "QUIT" keyword, followed by CRLF.
-
-            Possible responses:
-
-               "+ OK" and Close the connection
-
-   Replies
-
-      Greeting
-
-         The greeting is sent by the server as soon as the connection is
-         established.  The greeting is a plus sign, followed by the
-         protocol name ("POP2"), followed by the server host name,
-         optionally followed by text, and ending with a CRLF.
-
-      +
-
-         The success or plus sign response indicates successful
-         completion of the operation specified in the command.  The
-         success response is a plus sign, optionally followed by text,
-         and ending with a CRLF.
-
-      -
-
-         The failure or minus sign response indicates the failure of the
-         operation specified in the command.  The failure response is a
-         minus sign, optionally followed by text, and ending with a
-         CRLF.
-
-      =
-
-         The length or equal sign response tells the length in
-         characters of the message referenced by the command.  The
-         length response is a equal sign, followed by a number,
-         optionally followed by text, and ending with a CRLF.
-
-      #
-
-         The count or number sign response tells the number of messages
-         in a folder or mailbox referenced by the command.  The count
-         response is a number sign, followed by a number, optionally
-         followed by text, and ending with a CRLF.
-
-
-
-
-Butler, et. al.                                                [Page 10]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-   Timeouts
-
-      In any protocol of this type there have to be timeouts.  Neither
-      side wants to get stuck waiting forever for the other side
-      (particularly is the other side has gone crazy or crashed).
-
-      The client expects a reply to a command fairly quickly and so
-      should have a short timeout for this.  This timeout is called T1.
-
-         For some servers, it may take some processing to compute the
-         number of messages in a mailbox, or the length of a message, or
-         to reformat a stored message for transmission, so this time out
-         has to allow for such processing time.  Also care must be taken
-         not to timeout waiting for the completion of a RETR reply while
-         a long message is in fact being transfered.
-
-      The server expects the session to progress with some but not
-      excessive delay between commands and so should have a long timeout
-      waiting for the next command.  This time out is T2.
-
-         One model of use of this protocol is that any number of
-         different types of clients can be built with different ways of
-         interacting with the human user and the server, but still
-         expecting the client to open the connection to the server,
-         present a sequence of commands, and close the connection,
-         without waiting for intervention by the human user.  With such
-         client implementations, it is reasonable for the server to have
-         a fairly small value for timeout T2.
-
-         On the other hand, one could easily have the client be very
-         human user directed with the user making decisions between
-         commands.  This would cause arbitrary delays between client
-         commands to the server, and require the value of timeout T2 to
-         be quite large.
-
-Implementation Discussion
-
-   Comments on a Server on TOPS-20
-
-      On TOPS-20, a mailbox is a single file.  New messages are appended
-      to the file.  There is a separator line between messages.
-
-      The tricky part of implementing a POP2 server on TOPS-20 is to
-      provide for deleting messages.  This only has to be done for the
-      mailboxes (files) for which the user has write access.  The
-      problem is to avoid both (1) preventing other users from accessing
-      or updating the mailbox for long periods, and (2) accidentally
-      deleting a message the user has not seen.
-
-
-Butler, et. al.                                                [Page 11]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-      One suggestion is as follows:
-
-         When a mailbox is first selected, if the user has write access,
-         rename the mailbox file to some temporary name.  Thus new
-         messages will be placed in a new instance of the mailbox file.
-         Conduct all POP2 operation on the temporary mailbox file
-         (including deleting messages).  When the POP2 session is over
-         or another mailbox is selected, prepend any messages left
-         undeleted in the temporary file to the new instance of the
-         mailbox file.
-
-   Sizes
-
-      The maximum length of a command line is 512 characters (including
-      the command word and the CRLF).
-
-      The maximum length of a reply line is 512 characters (including
-      the success indicator (+, -, =, #) and the CRLF).
-
-      The maximum length of a text line is 1000 characters (including
-      CRLF).
-
-   ISI has developed a POP2 server for TOPS-20 and for Berkeley 4.2
-   Unix, and a POP2 client for an IBM-PC and for Berkeley 4.2 Unix.
-
-Extensions Not Supported
-
-   POP2 does not examine the internal data of messages.  In particular,
-   the server does not parse message headers.
-
-   The server doesn't have any state information (i.e., it doesn't know
-   from one session to the next what has happened).  For example, the
-   server doesn't know which messages were received since the last time
-   the user used POP2, so it can't send just the "new" messages.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-Butler, et. al.                                                [Page 12]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-Examples
-
-   Example 1:
-
-           Client                    Server
-           ------                    ------
-                                Wait for connection
-      Open connection  -->
-                           <--  + POP2 USC-ISIF.ARPA Server
-      HELO POSTEL SECRET -->
-                           <--  #2 messages in your mailbox
-      READ             -->   
-                           <--  =537 characters in message 1
-      RETR             -->   
-                           <--  [data of message 1]
-      ACKD             -->   
-                           <--  =234 characters in message 2
-      RETR             -->   
-                           <--  [data of message 2]
-      ACKD             -->   
-                           <--  =0 no more messages
-      QUIT             -->
-                           <--  + OK, bye, bye
-      Close connection --> <--  Close connection
-                                Go back to start
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-Butler, et. al.                                                [Page 13]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-   Example 2:
-
-           Client                    Server
-           ------                    ------
-                                Wait for connection
-      Open connection  -->
-                           <--  + POP2 ISI-VAXA.ARPA server here
-      HELO smith secret -->
-                           <--  #35 messages
-      FOLD /usr/spool/mail/smith -->
-                           <--  #27 messages
-      READ  27         -->   
-                           <--  =10123 characters in that message
-      RETR             -->   
-                           <--  [data of message 27]
-      ACKS             -->   
-                           <--  =0 no more messages
-      QUIT             -->
-                           <--  + bye, call again sometime.
-      Close connection --> <--  Close connection
-                                Go back to start
-
-   Example 3:
-
-           Client                    Server
-           ------                    ------
-                                Wait for connection
-      Open connection  -->
-                           <--  + POP2 ISI-VAXA.ARPA server here
-      HELO Jones secret -->
-                           <--  #0 messages
-      READ             -->   
-                           <--  Close connection
-      Close connection -->
-                                Go back to start
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-Butler, et. al.                                                [Page 14]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-Formal Syntax
-
-   <digit>    = 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
-
-   <letter>   = A | B | C | ... | Z
-                a | b | c | ... | z
-
-   <punct>    = ! | " | # | $ | % | & | ' | ( | ) | * |
-                + | , | - | / | : | < | = | > | ? | @ |
-                [ | ] | ^ | _ | ` | { | | | } | ~
-
-   <quote>    = \
-
-   <any>      = any one of the 128 ASCII codes
-
-   <CR>       = carriage return, code 10
-
-   <LF>       = line feed, code 13
-
-   <SP>       = space, code 32
-
-   <CRLF>     = <CR> <LF>
-
-   <print>    = <letter> | <digit> | <punct> | <quote> <any>
-
-   <char>     = <print> | <SP>
-
-   <word>     = <print> | <print> <word>
-
-   <string>   = <char> | <char> <string>
-
-   <ld>       = <letter> | <digit>
-
-   <ldh>      = <letter> | <digit> | -
-
-   <ldhs>     = <ldh> | <ldh> <ldhs>
-
-   <name>     = <letter> [ [ <ldhs> ] <ld> ]
-
-   <host>     =  <name> | <name> . <host>
-
-   <user>     = <word>
-
-   <password> = <word>
-
-   <mailbox>  = <string>
-
-   <number>   = <digit> | <digit> <number>
-
-
-Butler, et. al.                                                [Page 15]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-   <helo>     = HELO <SP> <user> <SP> <password> <CRLF>
-
-   <fold>     = FOLD <SP> <mailbox> <CRLF>
-
-   <read>     = READ [<SP> <number>] <CRLF>
-
-   <retr>     = RETR <CRLF>
-
-   <acks>     = ACKS <CRLF>
-
-   <ackd>     = ACKD <CRLF>
-
-   <nack>     = NACK <CRLF>
-
-   <quit>     = QUIT <CRLF>
-
-   <ok>       = + [<SP> <string>] <CRLF>
-
-   <err>      = - [<SP> <string>] <CRLF>
-
-   <count>    = # <number> [<SP> <string>] <CRLF>
-
-   <greet>    = + <SP> POP2 <SP> <host> [<SP> <string>] <CRLF>
-
-   <length>   = = <number> [<SP> <string>] <CRLF>
-
-   <command>  = <helo> | <fold> | <read> | <retr> |
-                <acks> | <ackd> | <nack> | <quit>
-
-   <reply>    = <ok> | <err> | <count> | <length> | <greet>
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-Butler, et. al.                                                [Page 16]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-Client State Diagram
-
-   
-                          |                    ^  + BYE  
-                          |  Open              |  -----  
-                          |           Greet    |  Close  
-                          V           -----    |         
-                      +-------+       QUIT    +-------+  
-                      | CALL  |-------------->| EXIT  |  
-                      +-------+               +-------+  
-                          |                       ^      
-                          |  Greet                |      
-                          |  -----                |      
-                          |  HELO                 |      
-              +---->+     |                       |      
-        #NNN  ^     |     |        #NNN           |      
-        ----  |     V     V        ----           |      
-        FOLD  |    +-------+       QUIT           |      
-              +<---| NMBR  |--------------------->+      
-                   +-------+                      ^      
-                    ^     |                       |      
-                    |     |  #NNN                 |      
-                    |     |  ----                 |      
-              =CCC  |     |  READ                 |      
-              ----  |     |                       |      
-              FOLD  |     |        =CCC           |      
-                    |     V        ----           |      
-        =CCC  +--->+-------+       QUIT           |      
-        ----  ^    | SIZE  |--------------------->+      
-        READ  +<---+-------+                             
-                    ^     |                              
-                    |     |  =CCC                        
-              data  |     |  ----                        
-              ----  |     |  RETR                        
-              ack   |     |                              
-                    |     V                              
-                   +-------+                             
-                   | XFER  |                             
-                   +-------+                             
-   
-
-
-
-
-
-
-
-
-
-
-Butler, et. al.                                                [Page 17]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-Server State Diagram
-
-   
-                       +<----------------------+  Close  
-                       |                       |  -----  
-               Listen  |                       |  Close  
-                       V                       |         
-                   +-------+                  +-------+  
-                   | LSTN  |                  | DONE  |  
-                   +-------+                  +-------+  
-                       |                          ^      
-                       |  Open                    |      
-                       |  -----                   |      
-                       |  Greet                   |      
-                       |                          |      
-                       |           QUIT           |      
-                       V           -----          |      
-                   +-------+       + BYE          |      
-                   | AUTH  |--------------------->+      
-                   +-------+                      ^      
-                       |                          |      
-                       |  HELO                    |      
-                       |  ----                    |      
-                       |  #NNN                    |      
-                       |                          |      
-                       |           QUIT           |      
-                       V           -----          |      
-        FOLD  +--->+-------+       + BYE          |      
-        ----  ^    | MBOX  |--------------------->+      
-        #NNN  +<---+-------+                      ^      
-                    ^     |                       |      
-                    |     |  READ                 |      
-              FOLD  |     |  ----                 |      
-              ----  |     |  =CCC                 |      
-              #NNN  |     |        QUIT           |      
-                    |     V        -----          |      
-        READ  +--->+-------+       + BYE          |      
-        ----  ^    | ITEM  |--------------------->+      
-        =CCC  +<---+-------+                             
-                    ^     |                              
-                    |     |  RETR                        
-              ack   |     |  ----                        
-              ----  |     |  data                        
-              =CCC  |     |                              
-                    |     V                              
-                   +-------+                             
-                   | NEXT  |                             
-                   +-------+                             
-
-
-Butler, et. al.                                                [Page 18]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-Combined Flow Diagram
-
-   
-   +----+                                                              
-   |CALL|<------------------------------------------------------------+
-   |LSTN|                                                             ^
-   +----+                                                             |
-    | Greet                                                           |
-    |                                                                 |
-    |  +----------------------------------------------------->+       |
-    |  ^ QUIT                                                 |       |
-    V  |                                                      V       |
-   +----+        +----+                                      +----+   |
-   |CALL| HELO   |NMBR|                                      |EXIT|   |
-   |AUTH|------->|AUTH|                                      |AUTH|   |
-   +----+        +----+                                      +----+   |
-                  | #NNN                                   + Bye |    |
-                  |                                              |    |
-                  |  +------------------------------------>+     |    |
-                  |  ^ QUIT                                |     |    |
-                  V  |                                     V     |    |
-            +--->+----+        +----+                     +----+ |    |
-       FOLD ^    |NMBR| READ   |SIZE|                     |EXIT| |    |
-       ---- |    |MBOX|------->|MBOX|                     |MBOX| |    |
-       #NNN +<---+----+        +----+                     +----+ |    |
-                     ^           | =CCC                 + Bye |  |    |
-                     |           |                            |  |    |
-                FOLD +<--------+ | +------------------->+     |  |    |
-                ----           ^ | ^ QUIT               |     |  |    |
-                #NNN           | V |                    V     |  |    |
-                         +--->+-----+        +----+    +----+ |  |    |
-                    READ ^    |SIZE | RETR   |XFER|    |EXIT| |  |    |
-                    ---- |    | ITEM|------->|ITEM|    |ITEM| |  |    |
-                    =CCC +<---+-----+        +----+    +----+ |  |    |
-                                 ^             | data      |  |  |    |
-                                 |             |           |  |  |    |
-                            =CCC |             V     + Bye |  |  |    |
-                               +----+        +----+        |  |  |    |
-                               |SIZE|    Ack |XFER|        |  |  |    |
-                               |NEXT|<-------|NEXT|        |  |  |    |
-                               +----+        +----+        |  |  |    |
-                                                           |  |  |    |
-                                                           |  |  |    |
-                                                           V  V  V    |
-                                                          +-------+   |
-                                                          | EXIT  |-->+
-                                                          | DONE  |    
-                                                          +-------+    
-
-
-Butler, et. al.                                                [Page 19]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-Client Decision Table
-
-   
-          |            STATE                 |
-   -------+----------------------------------|
-   INPUT  | CALL | NMBR | SIZE | XFER | EXIT |
-   -------+----------------------------------|
-   Greet  |  2   |  1   |  1   |  1   |  6   |
-   -------+----------------------------------|
-   #NNN   |  1   |  3   |  1   |  1   |  6   |
-   -------+----------------------------------|
-   =CCC   |  1   |  1   |  4   |  1   |  6   |
-   -------+----------------------------------|
-   data   |  1   |  1   |  1   |  5   |  6   |
-   -------+----------------------------------|
-   + Bye  |  1   |  1   |  1   |  1   |  6   |
-   -------+----------------------------------|
-   Close  |  1   |  1   |  1   |  1   |  6   |
-   -------+----------------------------------|
-   other  |  1   |  1   |  1   |  1   |  6   |
-   -------+----------------------------------|
-   Timeout|  1   |  1   |  1   |  1   |  6   |
-   -------+----------------------------------|
-   
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-Butler, et. al.                                                [Page 20]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-   Actions:
-
-      1.  This is garbage.  Send "QUIT", and go to EXIT state.
-
-      2.  (a) If the greeting is right then send "HELO"
-              and go to NMBR state,
-          (b) Else send "QUIT" and go to EXIT state.
-
-      3.  (a) If user wants this folder and NNN > 0
-              then send "READ" and go to SIZE state,
-          (b) If user wants a this folder and NNN = 0
-              then send "QUIT" and go to EXIT state,
-          (c) If user wants a different folder
-              then send "FOLD" and go to NMBR state.
-
-      4.  (a) If user wants this message and CCC > 0
-              then send "RETR" and go to XFER state,
-          (b) If user wants a this message and CCC = 0
-              then send "QUIT" and go to EXIT state,
-          (c) If user wants a different message
-              then send "READ" and go to SIZE state.
-
-      5.  (a) If user wants this message kept
-              then send "ACKS" and go to SIZE state,
-          (b) If user wants a this message deleted
-              then send "ACKD" and go to SIZE state,
-          (c) If user wants a this message again
-              then send "NACK" and go to SIZE state.
-
-      6.  Close the connection.
-
-
-
-
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-
-Butler, et. al.                                                [Page 21]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-Server Decision Table
-
-   
-          |              STATE                       
-   -------+----------------------------------------- 
-   INPUT  | LSTN | AUTH | MBOX | ITEM | NEXT | DONE |
-   -------+-----------------------------------------|
-   Open   |  2   |  1   |  1   |  1   |  1   |  1   |
-   -------+-----------------------------------------|
-   HELO   |  1   |  3   |  1   |  1   |  1   |  1   |
-   -------+-----------------------------------------|
-   FOLD   |  1   |  1   |  5   |  5   |  1   |  1   |
-   -------+-----------------------------------------|
-   READ   |  1   |  1   |  6   |  6   |  1   |  1   |
-   -------+-----------------------------------------|
-   RETR   |  1   |  1   |  1   |  7   |  1   |  1   |
-   -------+-----------------------------------------|
-   ACKS   |  1   |  1   |  1   |  1   |  8   |  1   |
-   -------+-----------------------------------------|
-   ACKD   |  1   |  1   |  1   |  1   |  8   |  1   |
-   -------+-----------------------------------------|
-   NACK   |  1   |  1   |  1   |  1   |  8   |  1   |
-   -------+-----------------------------------------|
-   QUIT   |  1   |  4   |  4   |  4   |  1   |  1   |
-   -------+-----------------------------------------|
-   Close  |  1   |  1   |  1   |  1   |  1   |  9   |
-   -------+-----------------------------------------|
-   other  |  1   |  1   |  1   |  1   |  1   |  1   |
-   -------+-----------------------------------------|
-   Timeout|      |  1   |  1   |  1   |  1   |  1   |
-   -------+-----------------------------------------|
-   
-
-
-
-
-
-
-
-
-
-
-
-
-
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-
-
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-
-Butler, et. al.                                                [Page 22]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-   Actions:
-
-      1.  This is garbage.  Send "- error", and Close the connection.
-
-      2.  Send the greeting. Go to AUTH state.
-
-      3.  (a) If authorized user then send "#NNN" and go tp MBOX state,
-          (b) Else send "- error" and Close the connection.
-
-      4.  Send "+ Bye" and go to DONE state.
-
-      5.  Send "+NNN" and go to MBOX state.
-
-      6.  Send "=CCC" and go to ITEM state.
-
-      7.  If message exists then send the data and got to NEXT state,
-          Else Close the connection.
-
-      8.  Do what ACKS/ACKD/NACK require and go to ITEM state.
-
-      9.  Close the connection.
-
-
-
-
-
-
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-
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-
-
-
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-
-Butler, et. al.                                                [Page 23]
-
-
-
-RFC 937                                                    February 1985
-Post Office Protocol
-
-
-Acknowledgment
-
-   We would like to acknowledge the helpful comments that we received on
-   the first version of POP described in RFC 918, and the draft of POP2
-   distributed to interested parties.
-
-References
-
-   [1]  Postel, J., "Simple Mail Transfer Protocol", RFC 821,
-   USC/Information Sciences Institute, August 1982.
-
-   [2]  Crocker, D., "Standard for the Format of ARPA-Internet Text
-   Messages", RFC 822, University of Delaware, August 1982.
-
-   [3]  Reynolds, J.K., "Post Office Protocol", RFC 918, USC/Information
-   Sciences Institute, October 1984.
-
-   [4]  Reynolds, J.K., and J. Postel, "Assigned Numbers", RFC 923,
-   USC/Information Sciences Institute, October 1984.
-
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-Butler, et. al.                                                [Page 24]
-