Network Working Group Greg Vaudreuil
Internet Draft Octel Network Services
Expires: 6/1/95 December 29, 1994
Enhanced Mail System Status Codes
<draft-ietf-notary-status-00.txt>
1. Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
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nic.nordu.net (Europe), ftp.isi.edu (US West Coast), or
munnari.oz.au (Pacific Rim).Introduction
2. Overview
SMTP [RFC-821] error codes have been proposed as a base for use
in delivery status notifications to indicate the full range of
possible mail delivery errors. Because SMTP does not indicate
the full range of transport or system level errors, the set of
codes was extended. This extension has several limitations for
which this proposal was created to avoid.
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 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
Internet Draft Mail System Status Codes December 29, 1994
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.
Status Codes 3.
This document defines a new set of status codes to report
delivery status in the DSN. The syntax of the new status codes is
defined as:
Status-Code = 1*Digit "." 1*Digit "." 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 system errors 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 (1)
Success specifies that the DSN is reporting a positive delivery
action. Detail digits may provide notification of
transformations required for delivery.
Permanent Failure (2)
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.
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Persistent Transient Failure (3)
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.
A client must recognize and report based on the first digit even
where subsequent digits are unrecognized.
The second digit classifies the subject of 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 greater detail about the status and is
defined relative to the subject of the status as indicated by the
second digit.
The following section defines and describes the detail status
code digits.
Other or Undefined Status (0) 1 3.
There is no additional detail available for other or undefined
status codes. Only the value "0" is defined.
3. Address Status (1) 2
The address status reports problems with the address specified.
It may include address syntax or validity.
2 3. .1 Other Address Status (1.0)
Something about the address specified in the message caused this
DSN.
.2 Bad mailbox address (1.1) 2 3.
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.
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Bad system address (1.2) 2.3 3.
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.
Bad mailbox address syntax (1.3) 2.4 3.
The address was syntactically invalid. This can apply to any
field in the address. This code is only useful for permanent
failures.
Mailbox address ambiguous (1.4) .5 3.2
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.
Mailbox Status (2) 3 3.
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.
Other or undefined mailbox status (2.0) 3.1 3.
The mailbox exists, but something about the destination mailbox
has cause the sending of this DSN.
3 Mailbox disabled, not accepting messages (2.1) .2 3.
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.
Mailbox full (2.2) 3.3 3.
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.
3 Message length exceeds administrative limit (2.3) 3. .4
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.
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Mailing list expansion problem (2.4) 3.5 3.
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.
System Status (3) 3.4
System status indicates that something having to do with the
destination system has cause this DSN. System issues are assumed
to be under the general control of the system administrator.
.1 Other or undefined system status (3.0) 4 3.
The destination system exists and normally accepts mail, but is
something about the system has caused the generation of this DSN.
System full (3.1) .2 3.4
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.
System not accepting network messages (3.2) .3 3.4
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.
System not capable of selected features (3.3) .4 4 3.
Selected message features specified for the message are not
supported by the destination system. This is useful only as a
permanent error.
Message too big for system (3.4) .5 4 3.
The message is larger than the system can handle, either for
physical or administrative reasons. This is useful only as a
permanent error.
Network and Routing Status (4) 5 3.
The networking or routing codes report status about the delivery
system itself, both the network and intermediate processing.
.1 5 3. 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.
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No answer from host (4.1) 5.2 3.
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.
.3 Bad connection (4.2) 3.5
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.
Routing server failure (4.3) .4 3.5
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.
Unable to route (4.4) .5 3.5
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.
Network congestion (4.5) .6 3.5
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.
3. Routing loop detected (4.6) 5.7
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.
3. .8 5 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.
6 3. Protocol Status (5)
6 3. Other or undefined protocol status (0) .1
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.
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Invalid command (5.1) 6.2 3.
A command was issued which was either out of sequence or
otherwise unsupported. This is useful only as a permanent error.
3. Syntax error (5.2) 6.3
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 Too many recipients (5.3) 6 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.
Invalid command arguments (5.4) .5 6 3.
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.
Wrong protocol version (5.5) .6 3.6
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.
Message Content or Media Status (6) 3.7
7 Other or undefined media error (6.0) .1 3.
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.
Media not supported (6.1) 7.2 3.
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.
7 Conversion required and prohibited (6.2) .3 3.
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
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itself or the policy of the sending host. This is useful only as
a permanent error.
Conversion required but not supported (6.3) 7.4 3.
The message content must be converted to be forwarded but such
conversion is not possible 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.
Conversion with loss performed (4) 7.5 3.
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 for successful notification.
Security Status (7) 8 3.
.1 8 3. 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.
Delivery not authorized, message refused (7.1) .2 3.8
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.
8 Mailing list expansion prohibited (7.2) .3 3.
The sender is not authorized to send a message to the intended
mailing list. This is useful only as a permanent error.
.4 8 3. 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.
8 Security features not supported (7.4) .5 3.
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.
3. .6 Cryptographic failure (7.5) 8
A transport system otherwise authorized to validate or decrypt a
message in transport was unable to do so because necessary
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information such as key was not available or such information was
invalid. This is useful only as a permanent error.
Cryptographic algorithm not supported (7.6) 8.7 3.
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.
.8 Message integrity failure (7.7) 3.8
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.
References 4.
[RFC-821] Postel, J., "Simple Mail Transfer Protocol", STD 10,
RFC 821, USC/Information Sciences Institute, August 1982.
Security Consideration 5.
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.
Author's Address 6.
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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Appendix - Collected Status Codes 7.
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.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.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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1 Appendix - Existing SMTP Reply-Codes From RFC 821 7.
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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