Network Working Group Greg Vaudreuil
Internet Draft Octel Network Services
Expires: 6/16/95 January 24, 1995
Enhanced Mail System Status Codes
<draft-ietf-notary-status-01.txt>
Changes from Last Version
1) Numerious editiorial corrections and clarifications including a revised
overview section.
2) Several new error codes were added.
a) An additional status code was added for mailbox valid. It was
suggested that other mailbox status was too ambigious for use in a
positive delivery report.
b) An additional status code was added to indicate that the address
has changed and no forwarding address is available.
c) An additional status code was added to indicate that a conversion
required for delivery failed.
3) The BNF was updated more clearly express the allowable values for each
of the status code fields. The first digit was redefined to have the same
values as the SMTP error codes, values 2-Success, 4-Persistant temporary
failure, and 5-Permanant failure. This change was discussed and agreed to
in San Jose but was overlooked in the first ID posting.
1. 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 working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months and
may be updated, replaced, or obsoleted by other documents at any time. It
is inappropriate to use Internet- Drafts as reference material or to cite
them other than as "work in progress."
To learn the current status of any Internet-Draft, please check the "1id-
abstracts.txt" listing contained in the Internet- Drafts Shadow Directories
on ds.internic.net (US East Coast), nic.nordu.net (Europe), ftp.isi.edu (US
West Coast), or munnari.oz.au (Pacific Rim).Introduction
Internet Draft Mail System Status Codes January 24, 1995
2. 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 [2]. This document proposes a new set of status codes for
this purpose.
SMTP [1] 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 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 will 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 starts from 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. The detail
value has been separated by a period and replaced by a two digit integer.
This separation into an integer provides a virtually unbounded space for
future growth as well as visually indicates that the codes is not SMTP.
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3. Status Codes
This document defines a new set of status codes to report delivery status
in the DSN. These status codes are intended to be used for media and
language independent status reporting and not for system specific
diagnostics.
The syntax of the new status codes is defined as:
status-code = class "." subject "." detail
class = "2"/"4"/"5"
subject = 2*digit
detail = 2*digit
The status codes are explicit enumeration's of each of the three fields.
The codes space defined is intended to be extensible only by standards
track documents. Mail system specific status codes should be mapped as
closely to the standard status codes. Servers should send only defined,
registered status codes. System specific errors and diagnostics may be
carried in the DSN via protocol specific extension fields. Clients should
preserve the extensibility of the code space by reporting the general error
described in the second protocol digit when the specific detail is
unrecognized.
The first digit provides a broad classification of the status. The
enumerated values of this first digit are defined as:
Success (2)
Success specifies that the DSN is reporting a positive delivery action.
Detail digits may provide notification of transformations required for
delivery.
Persistent Transient Failure (4)
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.
Permanent Failure (5)
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 based on the first digit even where
subsequent digits are unrecognized.
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The second subject digit classifies the status. This digit applies to each
of the three classifications. The second digit, if recognized, must be
reported even if the additional detail provided by the third digit is not
recognized. The enumerated values for the second digit are:
Other or undefined status (0)
Addressing status (1)
Mailbox status (2)
System status (3)
Network and Routing Status (4)
Protocol Status (5)
Message Content or Media Status (6)
Security Status (7)
The detail value provides more information about the status and is defined
relative to the subject of the status as indicated by the second digit.
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4. Enumberated Status Codes
The following section defines and describes the detail status code digits.
4.1 Other or Undefined Status (0)
There is no additional detail available for other or undefined status
codes. The only detail digit defined is (0).
4.2 Address Status (1)
The address status reports on the specified address. It may include
address syntax or validity.
4.2.1 Other Address Status (1.0)
Something about the address specified in the message caused this DSN.
4.2.2 Bad mailbox address (1.1)
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.
4.2.3 Bad system address (1.2)
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.
4.2.4 Bad mailbox address syntax (1.3)
The address was syntactically invalid. This can apply to any field in the
address. This code is only useful for permanent failures.
4.2.5 Mailbox address ambiguous (1.4)
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.
This code is only useful for permanent failures.
4.2.6 Address Valid (1.5)
This mailbox address as specified was valid. This status code should be
used for positive delivery reports.
4.2.7 Mailbox has moved, No forwarding address (1.6)
The mailbox address is was valid but is not longer availableresident on the
system. This code is only useful for permanent failures.
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4.3 Mailbox Status (2)
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 individual recipient.
4.3.1 Other or undefined mailbox status (2.0)
The mailbox exists, but something about the destination mailbox has caused
the sending of this DSN.
4.3.2 Mailbox disabled, not accepting messages (2.1)
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.
4.3.3 Mailbox full (2.2)
The mailbox is full either because the user has exceeded an administrative
quota or the dedicated physical resources have been exceeded. 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.
4.3.4 Message length exceeds administrative limit (2.3)
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.
4.3.5 Mailing list expansion problem (2.4)
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.
4.3.6 System Status (3)
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 system administrator.
4.3.7 Other or undefined system status (3.0)
The destination system exists and normally accepts mail, but something
about the system has caused the generation of this DSN.
4.3.8 System full (3.1)
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.
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4.3.9 System not accepting network messages (3.2)
The host on which the mailbox is resident is not accepting messages.
Examples of such conditions include an immanent shutdown or system
maintenance. This is useful for both permanent and permanent transient
errors.
4.3.10 System not capable of selected features (3.3)
Selected message features specified for the message are not supported by
the destination system. This is useful only as a permanent error.
4.3.11 Message too big for system (3.4)
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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4.4 Network and Routing Status (4)
The networking or routing codes report status about the delivery system
itself, both the network and intermediate processing.
4.4.1 Other or undefined network or routing status (4.0)
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.
4.4.2 No answer from host (4.1)
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.
4.4.3 Bad connection (4.2)
The outbound connection was completed, but was otherwise unable to complete
the message transaction, either because of time-out, excessive packet loss,
or inadequate quality. This is useful only as a persistent transient error.
4.4.4 Routing server failure (4.3)
The network system was unable to determine the next hop for the message,
because a nameserver was unavailable to resolve the address or provide a
route. This is useful only as a persistent transient error.
4.4.5 Unable to route (4.4)
The network was unable to determine the next hop for the message because
the necessary routing information was unavailable from the routing server.
This is useful for both permanent and persistent transient errors.
4.4.6 Network congestion (4.5)
The network or system was unable to deliver the message because the network
was congested, or the queuing was overfilled. This is useful only as a
persistent transient error.
4.4.7 Routing loop detected (4.6)
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.
4.4.8 Delivery time expired (4.7)
The message was considered too old by the rejecting system, either because
it remained on that host too long or because the TTL value specified by the
sender of the message was exceeded. This is useful only as a persistent
transient error.
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4.5 Protocol Status (5)
4.5.1 Other or undefined protocol status (0)
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.
4.5.2 Invalid command (5.1)
A command was issued which was either out of sequence or otherwise
unsupported. This is useful only as a permanent error.
4.5.3 Syntax error (5.2)
A command was issued which could not be interpreted, either because the
syntax was wrong or the command was not supported. This is useful only as a
permanent error.
4.5.4 Too many recipients (5.3)
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. This is useful only as a
permanent error.
4.5.5 Invalid command arguments (5.4)
A valid 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.
4.5.6 Wrong protocol version (5.5)
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. This is useful only as a permanent error.
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4.6 Message Content or Media Status (6)
4.6.1 Other or undefined media error (6.0)
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.
4.6.2 Media not supported (6.1)
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.
4.6.3 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. This
is useful only as a permanent error.
4.6.4 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. This is useful only as a permanent error.
4.6.5 Conversion with loss performed (6.4)
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 is useful only for successful notification.
4.6.6 Conversion Failed (6.5)
A conversion was required but was unsucessful. This may be useful as a
permanant or persistant temporary notification.
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4.7 Security Status (7)
4.7.1 Other or undefined security status (7.0)
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.
4.7.2 Delivery not authorized, message refused (7.1)
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.
4.7.3 Mailing list expansion prohibited (7.2)
The sender is not authorized to send a message to the intended mailing
list. This is useful only as a permanent error.
4.7.4 Security conversion required but not possible (7.3)
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.
4.7.5 Security features not supported (7.4)
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.
4.7.6 Cryptographic failure (7.5)
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.
4.7.7 Cryptographic algorithm not supported (7.6)
A transport system otherwise authorized to validate or decrypt a message
was unable to do so because the necessary algorithm was not supported. This
is useful only as a permanent error.
4.7.8 Message integrity failure (7.7)
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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5. References
[RFC-821] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
USC/Information Sciences Institute, August 1982.
6. Security Consideration
This document describes a status code system with increased precision. Use
of these status codes may disclose information about how an internal mail
system is implemented beyond that currently available.
7. Author's Address
Gregory M. Vaudreuil
Octel Network Services
17060 Dallas Parkway
Suite 214
Dallas, TX 75248-1905
214-733-2722
Greg.Vaudreuil@ons.octel.com
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8. Appendix - Collected Status Codes
X.1.0 Other Address Status
X.1.1 Bad mailbox address
X.1.2 Bad system address
X.1.3 Bad mailbox address syntax
X.1.4 Mailbox address ambiguous
X.1.5 Mailbox address valid
X.1.6 Mailbox has moved
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 system status
X.3.1 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
X.7.7 Message integrity failure
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9. Appendix - Existing SMTP Reply-Codes From RFC 821
211 System status, or system help reply
214 Help message
[Information on how to use the receiver or the meaning of a
particular non-standard command; this reply is useful only
to the human user]
220 <domain> Service ready
221 <domain> Service closing transmission channel
250 Requested mail action okay, completed
251 User not local; will forward to <forward-path>
354 Start mail input; end with <CRLF>.<CRLF>
421 <domain> Service not available,
closing transmission channel
[This may be a reply to any command if the service knows it
must shut down]
450 Requested mail action not taken: mailbox unavailable
[E.g., mailbox busy]
451 Requested action aborted: local error in processing
452 Requested action not taken: insufficient system storage
500 Syntax error, command unrecognized
[This may include errors such as command line too long]
501 Syntax error in parameters or arguments
502 Command not implemented
503 Bad sequence of commands
504 Command parameter not implemented
550 Requested action not taken: mailbox unavailable
[E.g., mailbox not found, no access]
551 User not local; please try <forward-path>
552 Requested mail action aborted: exceeded storage allocation
553 Requested action not taken: mailbox name not allowed
[E.g., mailbox syntax incorrect]
554 Transaction failed
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