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+Network Working Group                                        G. Vaudreuil
+Request for Comments: 1893                         Octel Network Services
+Category: Standards Track                                    January 1996
+
+
+                   Enhanced Mail System Status Codes
+
+Status of this Memo
+
+   This document specifies an Internet standards track protocol for the
+   Internet community, and requests discussion and suggestions for
+   improvements.  Please refer to the current edition of the "Internet
+   Official Protocol Standards" (STD 1) for the standardization state
+   and status of this protocol.  Distribution of this memo is unlimited.
+
+1.   Overview
+
+   There currently is not a standard mechanism for the reporting of mail
+   system errors except for the limited set offered by SMTP and the
+   system specific text descriptions sent in mail messages.  There is a
+   pressing need for a rich machine readable status code for use in
+   delivery status notifications [DSN].  This document proposes a new
+   set of status codes for this purpose.
+
+   SMTP [SMTP] error codes have historically been used for reporting
+   mail system errors.  Because of limitations in the SMTP code design,
+   these are not suitable for use in delivery status notifications.
+   SMTP provides about 12 useful codes for delivery reports.  The
+   majority of the codes are protocol specific response codes such as
+   the 354 response to the SMTP data command.  Each of the 12 useful
+   codes are each overloaded to indicate several error conditions each.
+   SMTP suffers some scars from history, most notably the unfortunate
+   damage to the reply code extension mechanism by uncontrolled use.
+   This proposal facilitates future extensibility by requiring the
+   client to interpret unknown error codes according to the theory of
+   codes while requiring servers to register new response codes.
+
+   The SMTP theory of reply codes partitioned in the number space such a
+   manner that the remaining available codes will not provide the space
+   needed.  The most critical example is the existence of only 5
+   remaining codes for mail system errors.  The mail system
+   classification includes both host and mailbox error conditions.  The
+   remaining third digit space would be completely consumed as needed to
+   indicate MIME and media conversion errors and security system errors.
+
+   A revision to the SMTP theory of reply codes to better distribute the
+   error conditions in the number space will necessarily be incompatible
+   with SMTP.  Further, consumption of the remaining reply-code number
+
+
+
+Vaudreuil                   Standards Track                     [Page 1]
+
+RFC 1893                Mail System Status Codes            January 1996
+
+
+   space for delivery notification reporting will reduce the available
+   codes for new ESMTP extensions.
+
+   The following proposal is based on the SMTP theory of reply codes.
+   It adopts the success, permanent error, and transient error semantics
+   of the first value, with a further description and classification in
+   the second.  This proposal re-distributes the classifications to
+   better distribute the error conditions, such as separating mailbox
+   from host errors.
+
+2.   Status Codes
+
+   This document defines a new set of status codes to report mail system
+   conditions.  These status codes are intended to be used for media and
+   language independent status reporting.  They are not intended for
+   system specific diagnostics.
+
+   The syntax of the new status codes is defined as:
+
+          status-code = class "." subject "." detail
+          class = "2"/"4"/"5"
+          subject = 1*3digit
+          detail = 1*3digit
+
+   White-space characters and comments are NOT allowed within a status-
+   code.  Each numeric sub-code within the status-code MUST be expressed
+   without leading zero digits.
+
+   Status codes consist of three numerical fields separated by ".". The
+   first sub-code indicates whether the delivery attempt was successful.
+   The second sub-code indicates the probable source of any delivery
+   anomalies, and the third sub-code indicates a precise error
+   condition.
+
+   The codes space defined is intended to be extensible only by
+   standards track documents.  Mail system specific status codes should
+   be mapped as close as possible to the standard status codes.  Servers
+   should send only defined, registered status codes.  System specific
+   errors and diagnostics should be carried by means other than status
+   codes.
+
+   New subject and detail codes will be added over time.  Because the
+   number space is large, it is not intended that published status codes
+   will ever be redefined or eliminated.  Clients should preserve the
+   extensibility of the code space by reporting the general error
+   described in the subject sub-code when the specific detail is
+   unrecognized.
+
+
+
+
+Vaudreuil                   Standards Track                     [Page 2]
+
+RFC 1893                Mail System Status Codes            January 1996
+
+
+   The class sub-code provides a broad classification of the status.
+   The enumerated values the class are defined as:
+
+    2.X.X   Success
+
+       Success specifies that the DSN is reporting a positive delivery
+       action.  Detail sub-codes may provide notification of
+       transformations required for delivery.
+
+    4.X.X   Persistent Transient Failure
+
+       A persistent transient failure is one in which the message as
+       sent is valid, but some temporary event prevents the successful
+       sending of the message.  Sending in the future may be successful.
+
+    5.X.X   Permanent Failure
+
+       A permanent failure is one which is not likely to be resolved by
+       resending the message in the current form.  Some change to the
+       message or the destination must be made for successful delivery.
+
+   A client must recognize and report class sub-code even where
+   subsequent subject sub-codes are unrecognized.
+
+   The subject sub-code classifies the status.  This value applies to
+   each of the three classifications.  The subject sub-code, if
+   recognized, must be reported even if the additional detail provided
+   by the detail sub-code is not recognized.  The enumerated values for
+   the subject sub-code are:
+
+       X.0.X   Other or Undefined Status
+
+          There is no additional subject information available.
+
+       X.1.X   Addressing Status
+
+          The address status reports on the originator or destination
+          address.  It may include address syntax or validity.  These
+          errors can generally be corrected by the sender and retried.
+
+       X.2.X   Mailbox Status
+
+          Mailbox status indicates that something having to do with the
+          mailbox has cause this DSN.  Mailbox issues are assumed to be
+          under the general control of the recipient.
+
+
+
+
+
+
+Vaudreuil                   Standards Track                     [Page 3]
+
+RFC 1893                Mail System Status Codes            January 1996
+
+
+       X.3.X   Mail System Status
+
+          Mail system status indicates that something having to do
+          with the destination system has caused this DSN.  System
+          issues are assumed to be under the general control of the
+          destination system administrator.
+
+       X.4.X   Network and Routing Status
+
+          The networking or routing codes report status about the
+          delivery system itself.  These system components include any
+          necessary infrastructure such as directory and routing
+          services.  Network issues are assumed to be under the
+          control of the destination or intermediate system
+          administrator.
+
+       X.5.X   Mail Delivery Protocol Status
+
+          The mail delivery protocol status codes report failures
+          involving the message delivery protocol.  These failures
+          include the full range of problems resulting from
+          implementation errors or an unreliable connection.  Mail
+          delivery protocol issues may be controlled by many parties
+          including the originating system, destination system, or
+          intermediate system administrators.
+
+       X.6.X   Message Content or Media Status
+
+          The message content or media status codes report failures
+          involving the content of the message.  These codes report
+          failures due to translation, transcoding, or otherwise
+          unsupported message media.  Message content or media issues
+          are under the control of both the sender and the receiver,
+          both of whom must support a common set of supported
+          content-types.
+
+       X.7.X   Security or Policy Status
+
+          The security or policy status codes report failures
+          involving policies such as per-recipient or per-host
+          filtering and cryptographic operations.  Security and policy
+          status issues are assumed to be under the control of either
+          or both the sender and recipient.  Both the sender and
+          recipient must permit the exchange of messages and arrange
+          the exchange of necessary keys and certificates for
+          cryptographic operations.
+
+
+
+
+
+Vaudreuil                   Standards Track                     [Page 4]
+
+RFC 1893                Mail System Status Codes            January 1996
+
+
+3.   Enumerated Status Codes
+
+   The following section defines and describes the detail sub-code. The
+   detail value provides more information about the status and is
+   defined relative to the subject of the status.
+
+   3.1 Other or Undefined Status
+
+       X.0.0   Other undefined Status
+
+          Other undefined status is the only undefined error code. It
+          should be used for all errors for which only the class of the
+          error is known.
+
+   3.2 Address Status
+
+       X.1.0   Other address status
+
+          Something about the address specified in the message caused
+          this DSN.
+
+       X.1.1   Bad destination mailbox address
+
+          The mailbox specified in the address does not exist.  For
+          Internet mail names, this means the address portion to the
+          left of the "@" sign is invalid.  This code is only useful
+          for permanent failures.
+
+       X.1.2   Bad destination system address
+
+          The destination system specified in the address does not
+          exist or is incapable of accepting mail.  For Internet mail
+          names, this means the address portion to the right of the
+          "@" is invalid for mail.  This codes is only useful for
+          permanent failures.
+
+       X.1.3   Bad destination mailbox address syntax
+
+          The destination address was syntactically invalid.  This can
+          apply to any field in the address.  This code is only useful
+          for permanent failures.
+
+       X.1.4   Destination mailbox address ambiguous
+
+          The mailbox address as specified matches one or more
+          recipients on the destination system.  This may result if a
+          heuristic address mapping algorithm is used to map the
+          specified address to a local mailbox name.
+
+
+
+Vaudreuil                   Standards Track                     [Page 5]
+
+RFC 1893                Mail System Status Codes            January 1996
+
+
+       X.1.5   Destination address valid
+
+          This mailbox address as specified was valid.  This status
+          code should be used for positive delivery reports.
+
+       X.1.6   Destination mailbox has moved, No forwarding address
+
+          The mailbox address provided was at one time valid, but mail
+          is no longer being accepted for that address.  This code is
+          only useful for permanent failures.
+
+       X.1.7   Bad sender's mailbox address syntax
+
+          The sender's address was syntactically invalid.  This can
+          apply to any field in the address.
+
+       X.1.8   Bad sender's system address
+
+          The sender's system specified in the address does not exist
+          or is incapable of accepting return mail.  For domain names,
+          this means the address portion to the right of the "@" is
+          invalid for mail.
+
+   3.3 Mailbox Status
+
+       X.2.0   Other or undefined mailbox status
+
+          The mailbox exists, but something about the destination
+          mailbox has caused the sending of this DSN.
+
+       X.2.1   Mailbox disabled, not accepting messages
+
+          The mailbox exists, but is not accepting messages.  This may
+          be a permanent error if the mailbox will never be re-enabled
+          or a transient error if the mailbox is only temporarily
+          disabled.
+
+       X.2.2   Mailbox full
+
+          The mailbox is full because the user has exceeded a
+          per-mailbox administrative quota or physical capacity.  The
+          general semantics implies that the recipient can delete
+          messages to make more space available.  This code should be
+          used as a persistent transient failure.
+
+
+
+
+
+
+
+Vaudreuil                   Standards Track                     [Page 6]
+
+RFC 1893                Mail System Status Codes            January 1996
+
+
+       X.2.3   Message length exceeds administrative limit
+
+          A per-mailbox administrative message length limit has been
+          exceeded.  This status code should be used when the
+          per-mailbox message length limit is less than the general
+          system limit.  This code should be used as a permanent
+          failure.
+
+       X.2.4   Mailing list expansion problem
+
+          The mailbox is a mailing list address and the mailing list
+          was unable to be expanded.  This code may represent a
+          permanent failure or a persistent transient failure.
+
+   3.4 Mail system status
+
+       X.3.0   Other or undefined mail system status
+
+          The destination system exists and normally accepts mail, but
+          something about the system has caused the generation of this
+          DSN.
+
+       X.3.1   Mail system full
+
+          Mail system storage has been exceeded.  The general
+          semantics imply that the individual recipient may not be
+          able to delete material to make room for additional
+          messages.  This is useful only as a persistent transient
+          error.
+
+       X.3.2   System not accepting network messages
+
+          The host on which the mailbox is resident is not accepting
+          messages.  Examples of such conditions include an immanent
+          shutdown, excessive load, or system maintenance.  This is
+          useful for both permanent and permanent transient errors.
+
+       X.3.3   System not capable of selected features
+
+          Selected features specified for the message are not
+          supported by the destination system.  This can occur in
+          gateways when features from one domain cannot be mapped onto
+          the supported feature in another.
+
+
+
+
+
+
+
+
+Vaudreuil                   Standards Track                     [Page 7]
+
+RFC 1893                Mail System Status Codes            January 1996
+
+
+       X.3.4   Message too big for system
+
+          The message is larger than per-message size limit.  This
+          limit may either be for physical or administrative reasons.
+          This is useful only as a permanent error.
+
+       X.3.5 System incorrectly configured
+
+          The system is not configured in a manner which will permit
+          it to accept this message.
+
+   3.5 Network and Routing Status
+
+       X.4.0   Other or undefined network or routing status
+
+          Something went wrong with the networking, but it is not
+          clear what the problem is, or the problem cannot be well
+          expressed with any of the other provided detail codes.
+
+       X.4.1   No answer from host
+
+          The outbound connection attempt was not answered, either
+          because the remote system was busy, or otherwise unable to
+          take a call.  This is useful only as a persistent transient
+          error.
+
+       X.4.2   Bad connection
+
+          The outbound connection was established, but was otherwise
+          unable to complete the message transaction, either because
+          of time-out, or inadequate connection quality. This is
+          useful only as a persistent transient error.
+
+       X.4.3   Directory server failure
+
+          The network system was unable to forward the message,
+          because a directory server was unavailable.  This is useful
+          only as a persistent transient error.
+
+          The inability to connect to an Internet DNS server is one
+          example of the directory server failure error.
+
+       X.4.4   Unable to route
+
+          The mail system was unable to determine the next hop for the
+          message because the necessary routing information was
+          unavailable from the directory server. This is useful for
+          both permanent and persistent transient errors.
+
+
+
+Vaudreuil                   Standards Track                     [Page 8]
+
+RFC 1893                Mail System Status Codes            January 1996
+
+
+          A DNS lookup returning only an SOA (Start of Administration)
+          record for a domain name is one example of the unable to
+          route error.
+
+       X.4.5   Mail system congestion
+
+          The mail system was unable to deliver the message because
+          the mail system was congested. This is useful only as a
+          persistent transient error.
+
+       X.4.6   Routing loop detected
+
+          A routing loop caused the message to be forwarded too many
+          times, either because of incorrect routing tables or a user
+          forwarding loop. This is useful only as a persistent
+          transient error.
+
+       X.4.7   Delivery time expired
+
+          The message was considered too old by the rejecting system,
+          either because it remained on that host too long or because
+          the time-to-live value specified by the sender of the
+          message was exceeded. If possible, the code for the actual
+          problem found when delivery was attempted should be returned
+          rather than this code.  This is useful only as a persistent
+          transient error.
+
+   3.6 Mail Delivery Protocol Status
+
+       X.5.0   Other or undefined protocol status
+
+          Something was wrong with the protocol necessary to deliver
+          the message to the next hop and the problem cannot be well
+          expressed with any of the other provided detail codes.
+
+       X.5.1   Invalid command
+
+          A mail transaction protocol command was issued which was
+          either out of sequence or unsupported.  This is useful only
+          as a permanent error.
+
+       X.5.2   Syntax error
+
+          A mail transaction protocol command was issued which could
+          not be interpreted, either because the syntax was wrong or
+          the command is unrecognized. This is useful only as a
+          permanent error.
+
+
+
+
+Vaudreuil                   Standards Track                     [Page 9]
+
+RFC 1893                Mail System Status Codes            January 1996
+
+
+       X.5.3   Too many recipients
+
+          More recipients were specified for the message than could
+          have been delivered by the protocol.  This error should
+          normally result in the segmentation of the message into two,
+          the remainder of the recipients to be delivered on a
+          subsequent delivery attempt.  It is included in this list in
+          the event that such segmentation is not possible.
+
+       X.5.4   Invalid command arguments
+
+          A valid mail transaction protocol command was issued with
+          invalid arguments, either because the arguments were out of
+          range or represented unrecognized features. This is useful
+          only as a permanent error.
+
+       X.5.5   Wrong protocol version
+
+          A protocol version mis-match existed which could not be
+          automatically resolved by the communicating parties.
+
+   3.7 Message Content or Message Media Status
+
+       X.6.0   Other or undefined media error
+
+          Something about the content of a message caused it to be
+          considered undeliverable and the problem cannot be well
+          expressed with any of the other provided detail codes.
+
+       X.6.1   Media not supported
+
+          The media of the message is not supported by either the
+          delivery protocol or the next system in the forwarding path.
+          This is useful only as a permanent error.
+
+       X.6.2   Conversion required and prohibited
+
+          The content of the message must be converted before it can
+          be delivered and such conversion is not permitted.  Such
+          prohibitions may be the expression of the sender in the
+          message itself or the policy of the sending host.
+
+       X.6.3   Conversion required but not supported
+
+          The message content must be converted to be forwarded but
+          such conversion is not possible or is not practical by a
+          host in the forwarding path.  This condition may result when
+          an ESMTP gateway supports 8bit transport but is not able to
+
+
+
+Vaudreuil                   Standards Track                    [Page 10]
+
+RFC 1893                Mail System Status Codes            January 1996
+
+
+          downgrade the message to 7 bit as required for the next hop.
+
+       X.6.4   Conversion with loss performed
+
+          This is a warning sent to the sender when message delivery
+          was successfully but when the delivery required a conversion
+          in which some data was lost.  This may also be a permanant
+          error if the sender has indicated that conversion with loss
+          is prohibited for the message.
+
+       X.6.5   Conversion Failed
+
+          A conversion was required but was unsuccessful.  This may be
+          useful as a permanent or persistent temporary notification.
+
+   3.8 Security or Policy Status
+
+       X.7.0   Other or undefined security status
+
+          Something related to security caused the message to be
+          returned, and the problem cannot be well expressed with any
+          of the other provided detail codes.  This status code may
+          also be used when the condition cannot be further described
+          because of security policies in force.
+
+       X.7.1   Delivery not authorized, message refused
+
+          The sender is not authorized to send to the destination.
+          This can be the result of per-host or per-recipient
+          filtering.  This memo does not discuss the merits of any
+          such filtering, but provides a mechanism to report such.
+          This is useful only as a permanent error.
+
+       X.7.2   Mailing list expansion prohibited
+
+          The sender is not authorized to send a message to the
+          intended mailing list. This is useful only as a permanent
+          error.
+
+       X.7.3   Security conversion required but not possible
+
+          A conversion from one secure messaging protocol to another
+          was required for delivery and such conversion was not
+          possible. This is useful only as a permanent error.
+
+
+
+
+
+
+
+Vaudreuil                   Standards Track                    [Page 11]
+
+RFC 1893                Mail System Status Codes            January 1996
+
+
+       X.7.4   Security features not supported
+
+          A message contained security features such as secure
+          authentication which could not be supported on the delivery
+          protocol. This is useful only as a permanent error.
+
+       X.7.5   Cryptographic failure
+
+          A transport system otherwise authorized to validate or
+          decrypt a message in transport was unable to do so because
+          necessary information such as key was not available or such
+          information was invalid.
+
+       X.7.6   Cryptographic algorithm not supported
+
+          A transport system otherwise authorized to validate or
+          decrypt a message was unable to do so because the necessary
+          algorithm was not supported.
+
+       X.7.7   Message integrity failure
+
+          A transport system otherwise authorized to validate a
+          message was unable to do so because the message was
+          corrupted or altered.  This may be useful as a permanent,
+          transient persistent, or successful delivery code.
+
+4.   References
+
+   [SMTP] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
+       USC/Information Sciences Institute, August 1982.
+
+   [DSN] Moore, K., and G. Vaudreuil, "An Extensible Message Format for
+       Delivery Status Notifications", RFC 1894, University of
+       Tennessee, Octel Network Services, January 1996.
+
+5.   Security Considerations
+
+   This document describes a status code system with increased
+   precision.  Use of these status codes may disclose additional
+   information about how an internal mail system is implemented beyond
+   that currently available.
+
+6.   Acknowledgments
+
+   The author wishes to offer special thanks to Harald Alvestrand, Marko
+   Kaittola, and Keith Moore for their extensive review and constructive
+   suggestions.
+
+
+
+
+Vaudreuil                   Standards Track                    [Page 12]
+
+RFC 1893                Mail System Status Codes            January 1996
+
+
+7.   Author's Address
+
+   Gregory M. Vaudreuil
+   Octel Network Services
+   17060 Dallas Parkway
+   Suite 214
+   Dallas, TX 75248-1905
+
+   Voice/Fax: +1-214-733-2722
+   EMail: Greg.Vaudreuil@Octel.com
+
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+Vaudreuil                   Standards Track                    [Page 13]
+
+RFC 1893                Mail System Status Codes            January 1996
+
+
+8.   Appendix - Collected Status Codes
+
+       X.1.0     Other address status
+       X.1.1     Bad destination mailbox address
+       X.1.2     Bad destination system address
+       X.1.3     Bad destination mailbox address syntax
+       X.1.4     Destination mailbox address ambiguous
+       X.1.5     Destination mailbox address valid
+       X.1.6     Mailbox has moved
+       X.1.7     Bad sender's mailbox address syntax
+       X.1.8     Bad sender's system address
+
+       X.2.0     Other or undefined mailbox status
+       X.2.1     Mailbox disabled, not accepting messages
+       X.2.2     Mailbox full
+       X.2.3     Message length exceeds administrative limit.
+       X.2.4     Mailing list expansion problem
+
+       X.3.0     Other or undefined mail system status
+       X.3.1     Mail system full
+       X.3.2     System not accepting network messages
+       X.3.3     System not capable of selected features
+       X.3.4     Message too big for system
+
+       X.4.0     Other or undefined network or routing status
+       X.4.1     No answer from host
+       X.4.2     Bad connection
+       X.4.3     Routing server failure
+       X.4.4     Unable to route
+       X.4.5     Network congestion
+       X.4.6     Routing loop detected
+       X.4.7     Delivery time expired
+
+       X.5.0     Other or undefined protocol status
+       X.5.1     Invalid command
+       X.5.2     Syntax error
+       X.5.3     Too many recipients
+       X.5.4     Invalid command arguments
+       X.5.5     Wrong protocol version
+
+       X.6.0     Other or undefined media error
+       X.6.1     Media not supported
+       X.6.2     Conversion required and prohibited
+       X.6.3     Conversion required but not supported
+       X.6.4     Conversion with loss performed
+       X.6.5     Conversion failed
+
+
+
+
+
+Vaudreuil                   Standards Track                    [Page 14]
+
+RFC 1893                Mail System Status Codes            January 1996
+
+
+       X.7.0     Other or undefined security status
+       X.7.1     Delivery not authorized, message refused
+       X.7.2     Mailing list expansion prohibited
+       X.7.3     Security conversion required but not possible
+       X.7.4     Security features not supported
+       X.7.5     Cryptographic failure
+       X.7.6     Cryptographic algorithm not supported
+       X.7.7     Message integrity failure
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+Vaudreuil                   Standards Track                    [Page 15]
+