



       Network Working Group                                 Greg Vaudreuil
       Internet Draft                                Octel Network Services
       Expires: 11/5/1995                                       May 5, 1995


                        Enhanced Mail System Status Codes

                        <draft-ietf-notary-status-03.txt>

       Status of this Memo

       This document is an Internet-Draft.  Internet-Drafts are working
       documents of the Internet Engineering Task Force (IETF), its areas,
       and its working groups.  Note that other groups may also distribute
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       Internet-Drafts are draft documents valid for a maximum of six
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       To learn the current status of any Internet-Draft, please check the
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       Rim).
       Internet Draft       Mail System Status Codes           May 5, 1995

     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 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.













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     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.

       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


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          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.

       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.




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       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.






































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     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.











































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     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 domain
          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 domain 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.

       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.


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     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 either because the user has exceeded an
          administrative quota.  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.

       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.
























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     3.4 Mail system status

       X.3.0   Other or undefined mail system status (3.0)

          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.

       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.























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     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.

          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.




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       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. This is useful only as a persistent transient error.


















































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     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.

       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 downgrading one of the communicating
          parties.  This should never happen in ESMTP.















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     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 the either the
          delivery protocol or a host in the forwarding path. This is
          useful only as a permanent error.

       X.6.2   Conversion required and prohibited (6.2)

          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 (6.3)

          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 a relay supports
          ESMTP transport but not MIME downgrade.

       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.

       X.6.5   Conversion Failed

          A conversion was required but was unsuccessful.  This may be
          useful as a permanent or persistent temporary notification.


















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     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.

       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. This is useful only as a permanent error.

       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.


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     4.   References

       [SMTP] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
       USC/Information Sciences Institute, August 1982.

       [DSN] Moore, K., Vaudreuil, G., "An Extensible Message Format for
       Delivery Status Notifications", Internet-Draft.

     5.   Security Consideration

       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 thank Harald Alvestrand, Marko
       Kaittola, and Keith Moore for their extensive review and
       constructive suggestions.

     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
       Greg.Vaudreuil@Octel.com


























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     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

       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


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       X.7.7     Message integrity failure























































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