As per Relevance of the word parameter, we have this rfc below:
Network Working Group K.
Request for Comments: 1891 University of
Category: Standards Track January 1996
SMTP Service
for Delivery Status
Status of this
This document specifies an Internet standards track protocol for
Internet community, and requests discussion and suggestions
improvements. Please refer to the current edition of the "
Official Protocol Standards" (STD 1) for the standardization
and status of this protocol. Distribution of this memo is unlimited
1.
This memo defines an extension to the SMTP service, which allows
SMTP client to specify (a) that delivery status notifications (DSNs
should be generated under certain conditions, (b) whether
notifications should return the contents of the message, and (c
additional information, to be returned with a DSN, that allows
sender to identify both the recipient(s) for which the DSN
issued, and the transaction in which the original message was sent
Any questions, comments, and reports of defects or ambiguities
this specification may be sent to the mailing list for the
working group of the IETF, using the
. Requests to subscribe to the
list should be addressed to .
Implementors of this specification are encouraged to subscribe to
mailing list, so that they will quickly be informed of any
which might hinder interoperability
NOTE: This document is a Proposed Standard. If and when
protocol is submitted for Draft Standard status, any normative
(phrases containing SHOULD, SHOULD NOT, MUST, MUST NOT, or MAY)
this document will be re-evaluated in light of
experience, and are thus subject to change
2.
The SMTP protocol [1] requires that an SMTP server
notification of delivery failure, if it determines that a
cannot be delivered to one or more recipients. Traditionally,
notification consists of an ordinary Internet mail message (
defined by [2]), sent to the envelope sender address (the argument
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RFC 1891 SMTP Delivery Status Notifications January 1996
the SMTP MAIL command), containing an explanation of the error and
least the headers of the failed message
Experience with large mail distribution lists [3] indicates that
messages are often insufficient to diagnose problems, or even
determine at which host or for which recipients a problem occurred
In addition, the lack of a standardized format for
notifications in Internet mail makes it difficult to exchange
notifications with other message handling systems
Such experience has demonstrated a need for a delivery
notification service for Internet electronic mail, which
(a) is reliable, in the sense that any DSN request will either
honored at the time of final delivery, or result in a
that indicates that the request cannot be honored
(b) when both success and failure notifications are requested
provides an unambiguous and nonconflicting indication of
delivery of a message to a recipient succeeded or failed
(c) is stable, in that a failed attempt to deliver a DSN should
result in the transmission of another DSN over the network
(d) preserves sufficient information to allow the sender to
both the mail transaction and the recipient address which
the notification, even when mail is forwarded or gatewayed
foreign environments,
(e) interfaces acceptably with non-SMTP and non-822-based
systems, both so that notifications returned from foreign
systems may be useful to Internet users, and so that
notification requests from foreign environments may be honored
Among the requirements implied by this goal are the ability
request non-return-of-content, and the ability to specify
positive delivery notifications, negative delivery notifications
both, or neither, should be issued
In an attempt to provide such a service, this memo uses the
defined in [4] to define an extension to the SMTP protocol.
this mechanism, an SMTP client may request that an SMTP server
or not issue a delivery status notification (DSN) under
conditions. The format of a DSN is defined in [5].
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3. Framework for the Delivery Status Notification
The following service extension is therefore defined
(1) The name of the SMTP service extension is "Delivery
Notification";
(2) the EHLO keyword value associated with this extension is "DSN",
the meaning of which is defined in section 4 of this memo
(3) no parameters are allowed with this EHLO keyword value
(4) two optional parameters are added to the RCPT command, and
optional parameters are added to the MAIL command
An optional parameter for the RCPT command, using
esmtp-keyword "NOTIFY", (to specify the conditions under which
delivery status notification should be generated), is defined
section 5.1,
An optional parameter for the RCPT command, using
esmtp-keyword "ORCPT", (used to convey the "original
(sender-specified) recipient address), is defined in section 5.2,
An optional parameter for the MAIL command, using
esmtp-keyword "RET", (to request that DSNs containing
indication of delivery failure either return the entire
of a message or only the message headers), is defined in
5.3,
An optional parameter for the MAIL command, using
esmtp-keyword "ENVID", (used to propagate an identifier for
message transmission envelope, which is also known to the
and will, if present, be returned in any DSNs issued for
transmission), is defined in section 5.4;
(5) no additional SMTP verbs are defined by this extension
The remainder of this memo specifies how support for the
effects the behavior of a message transfer agent
4. The Delivery Status Notification service
An SMTP client wishing to request a DSN for a message may issue
EHLO command to start an SMTP session, to determine if the
supports any of several service extensions. If the server
with code 250 to the EHLO command, and the response includes the
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keyword DSN, then the Delivery Status Notification extension (
described in this memo) is supported
Ordinarily, when an SMTP server returns a positive (2xx) reply
in response to a RCPT command, it agrees to accept responsibility
either delivering the message to the named recipient, or sending
notification to the sender of the message indicating that
has failed. However, an extended SMTP ("ESMTP") server
implements this service extension will accept an optional
parameter with the RCPT command. If present, the NOTIFY
alters the conditions for generation of delivery status
from the default (issue notifications only on failure) specified
[1]. The ESMTP client may also request (via the RET parameter
whether the entire contents of the original message should
returned (as opposed to just the headers of that message), along
the DSN
In general, an ESMTP server which implements this service
will propagate delivery status notification requests when
mail to other SMTP-based MTAs which also support this extension,
make a "best effort" to ensure that such requests are honored
messages are passed into other environments
In order that any delivery status notifications thus generated
be meaningful to the sender, any ESMTP server which supports
extension will attempt to propagate the following information to
other MTAs that are used to relay the message, for use in
DSNs
(a) for each recipient, a copy of the original recipient address,
used by the sender of the message
This address need not be the same as the mailbox specified in
RCPT command. For example, if a message was originally
to A@B.C and later forwarded to A@D.E, after such forwarding
taken place, the RCPT command will specify a mailbox of A@D.E
However, the original recipient address remains A@B.C
Also, if the message originated from an environment which does
use Internet-style user@domain addresses, and was gatewayed
SMTP, the original recipient address will preserve the
form of the recipient address
(b) for the entire SMTP transaction, an envelope
string, which may be used by the sender to associate any
status notifications with the transaction used to send
original message
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5. Additional parameters for RCPT and MAIL
The extended RCPT and MAIL commands are issued by a client when
wishes to request a DSN from the server, under certain conditions
for a particular recipient. The extended RCPT and MAIL commands
identical to the RCPT and MAIL commands defined in [1], except
one or more of the following parameters appear after the sender
recipient address, respectively. The general syntax for
SMTP commands is defined in [4].
NOTE: Although RFC 822 ABNF is used to describe the syntax of
parameters, they are not, in the language of that document
"structured field bodies". Therefore, while parentheses MAY
within an emstp-value, they are not recognized as comment delimiters
The syntax for "esmtp-value" in [4] does not allow SP, "=",
characters, or characters outside the traditional ASCII range of 1-
127 decimal to be transmitted in an esmtp-value. Because the
and ORCPT parameters may need to convey values outside this range
the esmtp-values for these parameters are encoded as "xtext".
"xtext" is formally defined as follows
xtext = *( xchar / hexchar )
xchar = any ASCII CHAR between "!" (33) and "~" (126) inclusive
except for "+" and "=".
; "hexchar"s are intended to encode octets that cannot
; as ASCII characters within an esmtp-value
hexchar = ASCII "+" immediately followed by two upper
hexadecimal
When encoding an octet sequence as xtext
+ Any ASCII CHAR between "!" and "~" inclusive, except for "+" and "=",
MAY be encoded as itself. (A CHAR in this range MAY instead
encoded as a "hexchar", at the implementor's discretion.)
+ ASCII CHARs that fall outside the range above must be encoded
"hexchar".
5.1 The NOTIFY parameter of the ESMTP RCPT
A RCPT command issued by a client may contain the optional esmtp
keyword "NOTIFY", to specify the conditions under which the
server should generate DSNs for that recipient. If the
esmtp-keyword is used, it MUST have an associated esmtp-value
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formatted according to the following rules, using the ABNF of
822:
notify-esmtp-value = "NEVER" / 1#notify-list-
notify-list-element = "SUCCESS" / "FAILURE" / "DELAY
Notes
a. Multiple notify-list-elements, separated by commas, MAY appear in
NOTIFY parameter; however, the NEVER keyword MUST appear by itself
b. Any of the keywords NEVER, SUCCESS, FAILURE, or DELAY may be
in any combination of upper and lower case letters
The meaning of the NOTIFY parameter values is generally as follows
+ A NOTIFY parameter value of "NEVER" requests that a DSN not
returned to the sender under any conditions
+ A NOTIFY parameter value containing the "SUCCESS" or "FAILURE
keywords requests that a DSN be issued on successful delivery
delivery failure, respectively
+ A NOTIFY parameter value containing the keyword "DELAY" indicates
sender's willingness to receive "delayed" DSNs. Delayed DSNs may
issued if delivery of a message has been delayed for an unusual
of time (as determined by the MTA at which the message is delayed),
but the final delivery status (whether successful or failure)
be determined. The absence of the DELAY keyword in a NOTIFY
requests that a "delayed" DSN NOT be issued under any conditions
The actual rules governing interpretation of the NOTIFY parameter
given in section 6.
For compatibility with SMTP clients that do not use the
facility, the absence of a NOTIFY parameter in a RCPT command may
interpreted as either NOTIFY=FAILURE or NOTIFY=FAILURE,DELAY
5.2 The ORCPT parameter to the ESMTP RCPT
The ORCPT esmtp-keyword of the RCPT command is used to specify
"original" recipient address that corresponds to the actual
to which the message is to be delivered. If the ORCPT esmtp-
is used, it MUST have an associated esmtp-value, which consists
the original recipient address, encoded according to the rules below
The ABNF for the ORCPT parameter is
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orcpt-parameter = "ORCPT=" original-recipient-
original-recipient-address = addr-type ";"
addr-type =
The "addr-type" portion MUST be an IANA-registered electronic
address-type (as defined in [5]), while the "xtext" portion
an encoded representation of the original recipient address using
rules in section 5 of this document. The entire ORCPT parameter
be up to 500 characters in length
When initially submitting a message via SMTP, if the ORCPT
is used, it MUST contain the same address as the RCPT TO
(unlike the RCPT TO address, the ORCPT parameter will be encoded
xtext). Likewise, when a mailing list submits a message via SMTP
be distributed to the list subscribers, if ORCPT is used, the
parameter MUST match the new RCPT TO address of each recipient,
the address specified by the original sender of the message.)
The "addr-type" portion of the original-recipient-address is used
indicate the "type" of the address which appears in the
parameter value. However, the address associated with the
keyword is NOT constrained to conform to the syntax rules for
"addr-type".
Ideally, the "xtext" portion of the original-recipient-address
contain, in encoded form, the same sequence of characters that
sender used to specify the recipient. However, for a
gatewayed from an environment (such as X.400) in which a
address is not a simple string of printable characters,
representation of recipient address must be defined by
specification for gatewaying between DSNs and that environment
5.3 The RET parameter of the ESMTP MAIL
The RET esmtp-keyword on the extended MAIL command specifies
or not the message should be included in any failed DSN issued
this message transmission. If the RET esmtp-keyword is used, it
have an associated esmtp-value, which is one of the
keywords
FULL requests that the entire message be returned in any "failed
delivery status notification issued for this recipient
HDRS requests that only the headers of the message be returned
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The FULL and HDRS keywords may be spelled in any combination of
and lower case letters
If no RET parameter is supplied, the MTA MAY return either
headers of the message or the entire message for any DSN
indication of failed deliveries
Note that the RET parameter only applies to DSNs that
delivery failure for at least one recipient. If a DSN contains
indications of delivery failure, only the headers of the
should be returned
5.4 The ENVID parameter to the ESMTP MAIL
The ENVID esmtp-keyword of the SMTP MAIL command is used to
an "envelope identifier" to be transmitted along with the message
included in any DSNs issued for any of the recipients named in
SMTP transaction. The purpose of the envelope identifier is to
the sender of a message to identify the transaction for which the
was issued
The ABNF for the ENVID parameter is
envid-parameter = "ENVID="
The ENVID esmtp-keyword MUST have an associated esmtp-value.
meaning is assigned by the mail system to the presence or absence
this parameter or to any esmtp-value associated with this parameter
the information is used only by the sender or his user agent.
ENVID parameter MAY be up to 100 characters in length
5.5 Restrictions on the use of Delivery Status Notification
The RET and ENVID parameters MUST NOT appear more than once each
any single MAIL command. If more than one of either of
parameters appears in a MAIL command, the ESMTP server SHOULD
with "501 syntax error in parameters or arguments".
The NOTIFY and ORCPT parameters MUST NOT appear more than once in
RCPT command. If more than one of either of these parameters
in a RCPT command, the ESMTP server SHOULD respond with "501
error in parameters or arguments".
6. Conformance
The Simple Mail Transfer Protocol (SMTP) is used by Message
Agents (MTAs) when accepting, relaying, or gatewaying mail, as
as User Agents (UAs) when submitting mail to the mail
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system. The DSN extension to SMTP may be used to allow UAs to
the sender's requests as to when DSNs should be issued. A UA
claims to conform to this specification must meet
requirements as described below
Typically, a message transfer agent (MTA) which supports SMTP
assume, at different times, both the role of a SMTP client and
SMTP server, and may also provide local delivery, gatewaying
foreign environments, forwarding, and mailing list expansion. An
which, when acting as an SMTP server, issues the DSN keyword
response to the EHLO command, MUST obey the rules below for
"conforming SMTP client" when acting as a client, and a "
SMTP server" when acting as a server. The term "conforming MTA
refers to an MTA which conforms to this specification, independent
its role of client or server
6.1 SMTP protocol
The following rules apply to SMTP transactions in which any of
ENVID, NOTIFY, RET, or ORCPT keywords are used
(a) If an SMTP client issues a MAIL command containing a valid
parameter and associated esmtp-value and/or a valid RET
and associated esmtp-value, a conforming SMTP server MUST
the same reply-code as it would to the same MAIL command
the ENVID and/or RET parameters. A conforming SMTP server
NOT refuse a MAIL command based on the absence or presence
valid ENVID or RET parameters, or on their
esmtp-values
However, if the associated esmtp-value is not valid (i.e.
illegal characters), or if there is more than one ENVID or
parameter in a particular MAIL command, the server MUST issue
reply-code 501 with an appropriate message (e.g. "syntax error
parameter").
(b) If an SMTP client issues a RCPT command containing any
NOTIFY and/or ORCPT parameters, a conforming SMTP server
return the same response as it would to the same RCPT
without those NOTIFY and/or ORCPT parameters. A conforming
server MUST NOT refuse a RCPT command based on the presence
absence of any of these parameters
However, if any of the associated esmtp-values are not valid,
if there is more than one of any of these parameters in
particular RCPT command, the server SHOULD issue the response "501
syntax error in parameter".
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6.2 Handling of messages received via
This section describes how a conforming MTA should handle
messages received via SMTP
NOTE: A DSN MUST NOT be returned to the sender for any message
which the return address from the SMTP MAIL command was NULL ("<>"),
even if the sender's address is available from other sources (e.g
the message header). However, the MTA which would otherwise issue
DSN SHOULD inform the local postmaster of delivery failures
some appropriate mechanism that will not itself result in
generation of DSNs
DISCUSSION: RFC 1123, section 2.3.3 requires error notifications
be sent with a NULL return address ("reverse-path"). This creates
interesting situation when a message arrives with one or
nonfunctional recipient addresses in addition to a
return address. When delivery to one of the recipient
fails, the MTA will attempt to send a nondelivery notification to
return address, setting the return address on the notification
NULL. When the delivery of this notification fails, the
attempting delivery of that notification sees a NULL return address
If that MTA were not to inform anyone of the situation, the
message would be silently lost. Furthermore, a nonfunctional
address is often indicative of a configuration problem in
sender's MTA. Reporting the condition to the local postmaster
help to speed correction of such errors
6.2.1 Relay of messages to other conforming SMTP
The following rules govern the behavior of a conforming MTA,
relaying a message which was received via the SMTP protocol, to
SMTP server that supports the Delivery Status Notification
extension
(a) Any ENVID parameter included in the MAIL command when a message
received, MUST also appear on the MAIL command with which
message is relayed, with the same associated esmtp-value. If
ENVID parameter was included in the MAIL command when the
was received, the ENVID parameter MUST NOT be supplied when
message is relayed
(b) Any RET parameter included in the MAIL command when a message
received, MUST also appear on the MAIL command with which
message is relayed, with the same associated esmtp-value. If no
parameter was included in the MAIL command when the message
received, the RET parameter MUST NOT supplied when the message
relayed
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RFC 1891 SMTP Delivery Status Notifications January 1996
(c) If the NOTIFY parameter was supplied for a recipient when
message was received, the RCPT command issued when the message
relayed MUST also contain the NOTIFY parameter along with
associated esmtp-value. If the NOTIFY parameter was not
for a recipient when the message was received, the NOTIFY
MUST NOT be supplied for that recipient when the message is relayed
(d) If any ORCPT parameter was present in the RCPT command for
recipient when the message was received, an ORCPT parameter with
identical original-recipient-address MUST appear in the RCPT
issued for that recipient when relaying the message. (For example
the MTA therefore MUST NOT change the case of any
characters in an ORCPT parameter.)
If no ORCPT parameter was present in the RCPT command when
message was received, an ORCPT parameter MAY be added to the
command when the message is relayed. If an ORCPT parameter is
by the relaying MTA, it MUST contain the recipient address from
RCPT command used when the message was received by that MTA
6.2.2 Relay of messages to non-conforming SMTP
The following rules govern the behavior of a conforming MTA (in
role of client), when relaying a message which was received via
SMTP protocol, to an SMTP server that does not support the
Status Notification service extension
(a) ENVID, NOTIFY, RET, or ORCPT parameters MUST NOT be issued
relaying the message
(b) If the NOTIFY parameter was supplied for a recipient, with an esmtp
value containing the keyword SUCCESS, and the SMTP server returns
success (2xx) reply-code in response to the RCPT command, the
MUST issue a "relayed" DSN for that recipient
(c) If the NOTIFY parameter was supplied for a recipient with an esmtp
value containing the keyword FAILURE, and the SMTP server returns
permanent failure (5xx) reply-code in response to the RCPT command
the client MUST issue a "failed" DSN for that recipient
(d) If the NOTIFY parameter was supplied for a recipient with an esmtp
value of NEVER, the client MUST NOT issue a DSN for that recipient
regardless of the reply-code returned by the SMTP server. However
if the server returned a failure (5xx) reply-code, the client
inform the local postmaster of the delivery failure via
appropriate mechanism that will not itself result in the
of DSNs
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When attempting to relay a message to an SMTP server that does
support this extension, and if NOTIFY=NEVER was specified for
recipients of that message, a conforming SMTP client MAY relay
message for those recipients in a separate SMTP transaction,
an empty reverse-path in the MAIL command. This will prevent
from being issued for those recipients by MTAs that conform to [1].
(e) If a NOTIFY parameter was not supplied for a recipient, and the
server returns a success (2xx) reply-code in response to a
command, the client MUST NOT issue any DSN for that recipient
(f) If a NOTIFY parameter was not supplied for a recipient, and the
server returns a permanent failure (5xx) reply-code in response to
RCPT command, the client MUST issue a "failed" DSN for
recipient
6.2.3 Local delivery of
The following rules govern the behavior of a conforming MTA
successful delivery of a message that was received via the
protocol, to a local recipient's mailbox
"Delivery" means that the message has been placed in the recipient'
mailbox. For messages which are transmitted to a mailbox for
retrieval via IMAP [6], POP [7] or a similar message access protocol
"delivery" occurs when the message is made available to the
(POP, etc.) service, rather than when the message is retrieved by
recipient's user agent
Similarly, for a recipient address which corresponds to a
list exploder, "delivery" occurs when the message is made
to that list exploder, even though the list exploder might refuse
deliver that message to the list recipients
(a) If the NOTIFY parameter was supplied for that recipient, with
esmtp-value containing the SUCCESS keyword, the MTA MUST issue
"delivered" DSN for that recipient
(b) If the NOTIFY parameter was supplied for that recipient which
not contain the SUCCESS keyword, the MTA MUST NOT issue a DSN
that recipient
(c) If the NOTIFY parameter was not supplied for that recipient, the
MUST NOT issue a DSN
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6.2.4 Gatewaying a message into a foreign
The following rules govern the behavior of a conforming MTA,
gatewaying a message that was received via the SMTP protocol, into
foreign (non-SMTP) environment
(a) If the the foreign environment is capable of issuing
notifications under the conditions requested by the
parameter, and the conforming MTA can ensure that any
thus issued will be translated into a DSN and delivered to
original sender, then the MTA SHOULD gateway the message into
foreign environment, requesting notification under the
conditions, without itself issuing a DSN
(b) If a NOTIFY parameter was supplied with the SUCCESS keyword, but
destination environment cannot return an appropriate notification
successful delivery, the MTA SHOULD issue a "relayed" DSN for
recipient
(c) If a NOTIFY parameter was supplied with an esmtp-keyword of NEVER,
DSN MUST NOT be issued. If possible, the MTA SHOULD direct
destination environment to not issue delivery notifications for
recipient
(d) If the NOTIFY parameter was not supplied for a particular recipient
a DSN SHOULD NOT be issued by the gateway. The gateway
attempt to ensure that appropriate notification will be provided
the foreign mail environment if eventual delivery failure occurs
and that no notification will be issued on successful delivery
(e) When gatewaying a message into a foreign environment, the return-of
content conditions specified by any RET parameter are nonbinding
however, the MTA SHOULD attempt to honor the request using
mechanisms exist in the foreign environment
6.2.5 Delays in
If a conforming MTA receives a message via the SMTP protocol, and
unable to deliver or relay the message to one or more recipients
an extended length of time (to be determined by the MTA), it
issue a "delayed" DSN for those recipients, subject to the
conditions
(a) If the NOTIFY parameter was supplied for a recipient and its
included the DELAY keyword, a "delayed" DSN MAY be issued
(b) If the NOTIFY parameter was not supplied for a recipient,
"delayed" DSN MAY be issued
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RFC 1891 SMTP Delivery Status Notifications January 1996
(c) If the NOTIFY parameter was supplied which did not contain the
keyword, a "delayed" DSN MUST NOT be issued
NOTE: Although delay notifications are common in present-
electronic mail, a conforming MTA is never required to
"delayed" DSNs. The DELAY keyword of the NOTIFY parameter
provided to allow the SMTP client to specifically request (
omitting the DELAY parameter) that "delayed" DSNs NOT be issued
6.2.6 Failure of a conforming MTA to deliver a
The following rules govern the behavior of a conforming MTA
received a message via the SMTP protocol, and is unable to deliver
message to a recipient specified in the SMTP transaction
(a) If a NOTIFY parameter was supplied for the recipient with an esmtp
keyword containing the value FAILURE, a "failed" DSN MUST be
by the MTA
(b) If a NOTIFY parameter was supplied for the recipient which did
contain the value FAILURE, a DSN MUST NOT be issued for
recipient. However, the MTA MAY inform the local postmaster of
delivery failure via some appropriate mechanism which does
itself result in the generation of DSNs
(c) If no NOTIFY parameter was supplied for the recipient, a "failed
DSN MUST be issued
NOTE: Some MTAs are known to forward undeliverable messages to
local postmaster or "dead letter" mailbox. This is still
delivery failure, and does not diminish the requirement to issue
"failed" DSN under the conditions defined elsewhere in this memo.
a DSN is issued for such a recipient, the Action value MUST
"failed".
6.2.7 Forwarding, aliases, and mailing
Delivery of a message to a local email address usually causes
message to be stored in the recipient's mailbox. However,
commonly provide a facility where a local email address can
designated as an "alias" or "mailing list"; delivery to that
then causes the message to be forwarded to each of the (local
remote) recipient addresses associated with the alias or list. It
also common to allow a user to optionally "forward" her mail to
or more alternate addresses. If this feature is enabled, her mail
redistributed to those addresses instead of being deposited in
mailbox
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Following the example of [9] (section 5.3.6), this document
the difference between an "alias" and "mailing list" as follows:
forwarding a message to the addresses associated with an "alias",
envelope return address (e.g. SMTP MAIL FROM) remains intact
However, when forwarding a message to the addresses associated with
"mailing list", the envelope return address is changed to that of
administrator of the mailing list. This causes DSNs and
nondelivery reports resulting from delivery to the list members to
sent to the list administrator rather than the sender of the
message
The DSN processing for aliases and mailing lists is as follows
6.2.7.1 mailing
When a message is delivered to a list submission address (i.e.
in the list's mailbox for incoming mail, or accepted by the
that redistributes the message to the list subscribers), this
considered final delivery for the original message. If the
parameter for the list submission address contained the
keyword, a "delivered" DSN MUST be returned to the sender of
original message
NOTE: Some mailing lists are able to reject message submissions
based on the content of the message, the sender's address, or
other criteria. While the interface between such a mailing list
its MTA is not well-defined, it is important that DSNs NOT be
by both the MTA (to report successful delivery to the list), and
list (to report message rejection using a "failure" DSN.)
However, even if a "delivered" DSN was issued by the MTA, a
list which rejects a message submission MAY notify the sender
the message was rejected using an ordinary message instead of a DSN
Whenever a message is redistributed to an mailing list
(a) The envelope return address is rewritten to point to the
maintainer. This address MAY be that of a process that
DSNs and processes them automatically, but it MUST
unrecognized messages to the human responsible for the list
(b) The ENVID, NOTIFY, RET, and ORCPT parameters which accompany
redistributed message MUST NOT be derived from those of the
message
(c) The NOTIFY and RET parameters MAY be specified by the
postmaster or the list administrator. If ORCPT parameters
supplied during redistribution to the list subscribers, they
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contain the addresses of the list subscribers in the format used
the mailing list
6.2.7.2 single-recipient
Under normal circumstances, when a message arrives for an "alias
which has a single forwarding address, a DSN SHOULD NOT be issued
Any ENVID, NOTIFY, RET, or ORCPT parameters SHOULD be propagated
the message as it is redistributed to the forwarding address
6.2.7.3 multiple-recipient
An "alias" with multiple recipient addresses may be handled in any
the following ways
(a) Any ENVID, NOTIFY, RET, or ORCPT parameters are NOT propagated
relaying the message to any of the forwarding addresses. If
NOTIFY parameter for the alias contained the SUCCESS keyword,
MTA issues a "relayed" DSN. (In effect, the MTA treats the
as if it were being relayed into an environment that does
support DSNs.)
(b) Any ENVID, NOTIFY, RET, or ORCPT parameters (or the
requests if the message is gatewayed) are propagated to EXACTLY
of the forwarding addresses. No DSN is issued. (This
appropriate when aliasing is used to forward a message to
"vacation" auto-responder program in addition to the local mailbox.)
(c) Any ENVID, RET, or ORCPT parameters are propagated to all
addresses associated with that alias. The NOTIFY parameter
propagated to the forwarding addresses, except that it any
keyword is removed. If the original NOTIFY parameter for the
contained the SUCCESS keyword, an "expanded" DSN is issued for
alias. If the NOTIFY parameter for the alias did not contain
SUCCESS keyword, no DSN is issued for the alias
6.2.7.4 confidential forwarding
If it is desired to maintain the confidentiality of a recipient'
forwarding address, the forwarding may be treated as if it were
mailing list. A DSN will be issued, if appropriate, upon "delivery
to the recipient address specified by the sender. When the
is forwarded it will have a new envelope return address. Any
which result from delivery failure of the forwarded message will
be returned to the original sender of the message and thus not
the recipient's forwarding address
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RFC 1891 SMTP Delivery Status Notifications January 1996
6.2.8 DSNs describing delivery to multiple
A single DSN may describe attempts to deliver a message to
recipients of that message. If a DSN is issued for some
in an SMTP transaction and not for others according to the
above, the DSN SHOULD NOT contain information for recipients for
DSNs would not otherwise have been issued
6.3 Handling of messages from other
For messages which originated from "local" users (whatever
means), the specifications under which DSNs should be generated
be communicated to the MTA via any protocol agreed on between
sender's mail composer (user agent) and the MTA. The local MTA
then either relay the message, or issue appropriate delivery
notifications. However, if such requests are transmitted within
message itself (for example in the message headers), the
MUST be removed from the message before it is transmitted via SMTP
For messages gatewayed from non-SMTP sources and further relayed
SMTP, the gateway SHOULD, using the SMTP extensions described here
attempt to provide the delivery reporting conditions expected by
source mail environment. If appropriate, any DSNs returned to
source environment SHOULD be translated into the format expected
that environment
6.4 Implementation
A conforming MTA MUST accept ESMTP parameters of at least
following sizes
(a) ENVID parameter: 100 characters
(b) NOTIFY parameter: 28 characters
(c) ORCPT parameter: 500 characters
(d) RET parameter: 8 characters
The maximum sizes for the ENVID and ORCPT parameters are intended
be adequate for the transmission of "foreign" envelope identifier
original recipient addresses. However, user agents which use SMTP
a message submission protocol SHOULD NOT generate ENVID
which are longer than 38 characters in length
A conforming MTA MUST be able to accept SMTP command-lines which
at least 1036 characters long (530 characters for the ORCPT
NOTIFY parameters of the RCPT command, in addition to the 512
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RFC 1891 SMTP Delivery Status Notifications January 1996
characters required by [1]). If other SMTP extensions are
by the MTA, the MTA MUST be able to accept a command-line
enough for each SMTP command and any combination of ESMTP
which may be used with that command
7. Format of delivery
The format of delivery status notifications is defined in [5],
uses the framework defined in [8]. Delivery status notifications
to be returned to the sender of the original message as
below
7.1 SMTP Envelope to be used with delivery status
The DSN sender address (in the SMTP MAIL command) MUST be a
reverse-path ("<>"), as required by section 5.3.3 of [9]. The
recipient address (in the RCPT command) is copied from the
command which accompanied the message for which the DSN is
issued. When transmitting a DSN via SMTP, the RET parameter MUST
be used. The NOTIFY parameter MAY be used, but its value MUST
NEVER. The ENVID parameter (with a newly generated envelope-id
and/or ORCPT parameter MAY be used
7.2 Contents of the
A DSN is transmitted as a MIME message with a top-level content-
of multipart/report (as defined in [5]).
The multipart/report content-type may be used for any of
kinds of reports generated by the mail system. When multipart/
is used to convey a DSN, the report-type parameter of
multipart/report content-type is "delivery-status".
As described in [8], the first component of a multipart/
content-type is a human readable explanation of the report. For
DSN, the second component of the multipart/report is of content-
message/delivery-status (defined in [5]). The third component of
multipart/report consists of the original message or some
thereof. When the value of the RET parameter is FULL, the
message SHOULD be returned for any DSN which conveys notification
delivery failure. (However, if the length of the message is
than some implementation-specified length, the MTA MAY return
the headers even if the RET parameter specified FULL.) If a
contains no notifications of delivery failure, the MTA SHOULD
only the headers
The third component must have an appropriate content-type label
Issues concerning selection of the content-type are discussed in [8].
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RFC 1891 SMTP Delivery Status Notifications January 1996
7.3 Message/delivery-status
The message/delivery-status content-type defines a number of fields
with general specifications for their contents. The
requirements for any DSNs generated in response to a message
by the SMTP protocol by a conforming SMTP server, are in addition
the requirements defined in [5] for the message/delivery-status type
When generating a DSN for a message which was received via the
protocol, a conforming MTA will generate the following fields of
message/delivery-status body part
(a) if an ENVID parameter was present on the MAIL command, an Original
Envelope-ID field MUST be supplied, and the value associated
the ENVID parameter must appear in that field. If the message
received via SMTP with no ENVID parameter, the Original-Envelope-
field MUST NOT be supplied
Since the ENVID parameter is encoded as xtext, but the Original
Envelope-ID header is NOT encoded as xtext, the MTA must decode
xtext encoding when copying the ENVID value to the Original
Envelope-ID field
(b) The Reporting-MTA field MUST be supplied. If Reporting MTA
determine its fully-qualified Internet domain name, the MTA-name
type subfield MUST be "dns", and the field MUST contain the fully
qualified domain name of the Reporting MTA. If the fully-
Internet domain name of the Reporting MTA is not known (for example
for an SMTP server which is not directly connected to the Internet),
the Reporting-MTA field may contain any string identifying the MTA
however, in this case the MTA-name-type subfield MUST NOT be "dns".
A MTA-name-type subfield value of "x-local-hostname" is suggested
(c) Other per-message fields as defined in [5] MAY be supplied
appropriate
(d) If the ORCPT parameter was provided for this recipient,
Original-Recipient field MUST be supplied, with its value taken
the ORCPT parameter. If no ORCPT parameter was provided for
recipient, the Original-Recipient field MUST NOT appear
(e) The Final-Recipient field MUST be supplied. It MUST contain
recipient address from the message envelope. If the message
received via SMTP, the address-type will be "rfc822".
(f) The Action field MUST be supplied
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RFC 1891 SMTP Delivery Status Notifications January 1996
(g) The Status field MUST be supplied, using a status-code from [10].
If there is no specific code which suitably describes a
failure, either 4.0.0 (temporary failure), or 5.0.0 (
failure) MUST be used
(h) For DSNs resulting from attempts to relay a message to one or
recipients via SMTP, the Remote-MTA field MUST be supplied for
of those recipients. The mta-name-type subfields of those Remote
MTA fields will be "dns".
(i) For DSNs resulting from attempts to relay a message to one or
recipients via SMTP, the Diagnostic-Code MUST be supplied for
of those recipients. The diagnostic-type subfield will be "smtp".
See section 9.2(a) of this document for a description of the "smtp
diagnostic-code
(j) For DSNs resulting from attempts to relay a message to one or
recipients via SMTP, an SMTP-Remote-Recipient extension field MAY
supplied for each recipient, which contains the address of
recpient which was presented to the remote SMTP server
(k) Other per-recipient fields defined in [5] MAY appear,
appropriate
8.
The author wishes to thank Eric Allman, Harald Alvestrand,
Conklin, Bryan Costales, Peter Cowen, Dave Crocker, Roger Fajman,
Freed, Marko Kaittola, Steve Kille, John Klensin,
Kotsikonas, John Gardiner Myers, Julian Onions, Jacob Palme,
Rose, Greg Vaudreuil, and Klaus Weide for their suggestions
improvement of this document
Moore Standards Track [Page 20]
RFC 1891 SMTP Delivery Status Notifications January 1996
9. Appendix - Type-Name
The following type names are defined for use in DSN fields
by conforming SMTP-based MTAs
9.1 "rfc822" address-
The "rfc822" address-type is to be used when reporting
electronic mail address in the Original-Recipient and Final-
DSN fields
(a) address-type name: rfc822
(b) syntax for mailbox
RFC822 mailbox addresses are generally expected to be of the
[route] addr-
where "route" and "addr-spec" are defined in [2], and the "domain
portions of both "route" and "addr-spec" are fully-qualified
names that are registered in the DNS. However, an MTA MUST
modify an address obtained from the message envelope to force it
conform to syntax rules
(c) If addresses of this type are not composed entirely of
characters from the US-ASCII repertoire, a specification for how
are to be encoded as graphic US-ASCII characters in a DSN Original
Recipient or Final-Recipient DSN field
RFC822 addresses consist entirely of graphic characters from the US
ASCII repertoire, so no translation is necessary
9.2 "smtp" diagnostic-
The "smtp" diagnostic-type is to be used when reporting SMTP reply
codes in Diagnostic-Code DSN fields
(a) diagnostic-type name:
(b) A description of the syntax to be used for expressing
codes of this type as graphic characters from the US-ASCII repertoire
An SMTP diagnostic-code is of the
*( 3*DIGIT "-" *text ) 3*DIGIT SPACE *
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RFC 1891 SMTP Delivery Status Notifications January 1996
For a single-line SMTP reply to an SMTP command, the diagnostic-
SHOULD be an exact transcription of the reply. For multi-line
replies, it is necessary to insert a SPACE before each line
the first. For example, an SMTP reply of
550-mailbox
550 user has moved with no forwarding
could appear as follows in a Diagnostic-Code DSN field
Diagnostic-Code: smtp ; 550-mailbox
550 user has moved with no forwarding
(c) A list of valid diagnostic codes of this type and the meaning
each code
SMTP reply-codes are currently defined in [1], [4], and [9].
Additional codes may be defined by other RFCs
9.3 "dns" MTA-name-
The "dns" MTA-name-type should be used in the Reporting-MTA field
An MTA-name of type "dns" is a fully-qualified domain name. The
must be registered in the DNS, and the address Postmaster@{mta-name
must be valid
(a) MTA-name-type name:
(b) A description of the syntax of MTA names of this type, using BNF
regular expressions, ASN.1, or other non-ambiguous language
MTA names of type "dns" SHOULD be valid Internet domain names.
such domain names are not available, a domain-literal containing
internet protocol address is acceptable. Such domain
generally conform to the following syntax
domain = real-domain / domain-
real-domain = sub-domain *("." sub-domain
sub-domain =
domain-literal = "[" 1*3DIGIT 3("." 1*3DIGIT) "]"
where "atom" and "DIGIT" are defined in [2].
Moore Standards Track [Page 22]
RFC 1891 SMTP Delivery Status Notifications January 1996
(c) If MTA names of this type do not consist entirely of
characters from the US-ASCII repertoire, a specification for how an
name of this type should be expressed as a sequence of graphic US-
characters
MTA names of type "dns" consist entirely of graphic US-
characters, so no translation is needed
10. Appendix -
This example traces the flow of a single message addressed
multiple recipients. The message is sent by Alice@Pure-Heart.ORG
Bob@Big-Bucks.COM, Carol@Ivory.EDU, Dana@Ivory.EDU
Eric@Bombs.AF.MIL, Fred@Bombs.AF.MIL, and George@Tax-ME.GOV, with
variety of per-recipient options. The message is
delivered to Bob, Dana (via a gateway), Eric, and Fred.
fails for Carol and George
NOTE: Formatting rules for RFCs require that no line be longer
72 characters. Therefore, in the following examples, some
commands longer than 72 characters are printed on two lines, with
first line ending in "\". In an actual SMTP transaction, such
command would be sent as a single line (i.e. with no embedded CRLFs),
and without the "\" character that appears in these examples
10.1
Alice's user agent sends the message to the SMTP server at Pure
Heart.ORG. Note that while this example uses SMTP as a
submission protocol, other protocols could also be used
<<< 220 Pure-Heart.ORG SMTP server
>>> EHLO Pure-Heart.
<<< 250-Pure-Heart.
<<< 250-
<<< 250-
<<< 250
>>> MAIL FROM: RET=HDRS ENVID=QQ314159
<<< 250 sender
>>> RCPT TO: NOTIFY=SUCCESS \
ORCPT=rfc822;Bob@Big-Bucks.
<<< 250 recipient
>>> RCPT TO: NOTIFY=FAILURE \
ORCPT=rfc822;Carol@Ivory.
<<< 250 recipient
>>> RCPT TO: NOTIFY=SUCCESS,FAILURE \
ORCPT=rfc822;Dana@Ivory.
<<< 250 recipient
Moore Standards Track [Page 23]
RFC 1891 SMTP Delivery Status Notifications January 1996
>>> RCPT TO: NOTIFY=FAILURE \
ORCPT=rfc822;Eric@Bombs.AF.
<<< 250 recipient
>>> RCPT TO: NOTIFY=
<<< 250 recipient
>>> RCPT TO: NOTIFY=FAILURE \
ORCPT=rfc822;George@Tax-ME.
<<< 250 recipient
>>>
<<< 354 okay, send
>>> (message goes here
>>> .
<<< 250 message
>>>
<<< 221
10.2 Relay to Big-Bucks.
The SMTP at Pure-Heart.ORG then relays the message to Big-Bucks.COM
(For the purpose of this example, mail.Big-Bucks.COM is the
mail exchanger for Big-Bucks.COM).
<<< 220 mail.Big-Bucks.COM says
>>> EHLO Pure-Heart.
<<< 250-mail.Big-Bucks.
<<< 250
>>> MAIL FROM: RET=HDRS ENVID=QQ314159
<<< 250 sender
>>> RCPT TO: NOTIFY=SUCCESS \
ORCPT=rfc822;Bob@Big-Bucks.
<<< 250 recipient
>>>
<<< 354 send
>>> (message goes here
>>> .
<<< 250 message
>>>
<<< 221
10.3 Relay to Ivory.
The SMTP at Pure-Heart.ORG relays the message to Ivory.EDU, which (
it happens) is a gateway to a LAN-based mail system that accepts
mail and supports the DSN extension
<<< 220 Ivory.EDU gateway to FooMail(tm)
>>> EHLO Pure-Heart.
<<< 250-Ivory.
Moore Standards Track [Page 24]
RFC 1891 SMTP Delivery Status Notifications January 1996
<<< 250
>>> MAIL FROM: RET=HDRS ENVID=QQ314159
<<< 250
>>> RCPT TO: NOTIFY=FAILURE \
ORCPT=rfc822;Carol@Ivory.
<<< 550 error - no such
>>> RCPT TO: NOTIFY=SUCCESS,FAILURE \
ORCPT=rfc822;Dana@Ivory.
<<< 250 recipient
>>>
<<< 354 send message, end with '.'
>>> (message goes here
>>> .
<<< 250 message
>>>
<<< 221
Note that since the Ivory.EDU refused to accept mail
Carol@Ivory.EDU, and the sender specified NOTIFY=FAILURE,
sender-SMTP (in this case Pure-Heart.ORG) must generate a DSN
10.4 Relay to Bombs.AF.
The SMTP at Pure-Heart.ORG relays the message to Bombs.AF.MIL,
does not support the SMTP extension. Because the sender
NOTIFY=NEVER for recipient Fred@Bombs.AF.MIL, the SMTP at Pure
Heart.ORG chooses to send the message for that recipient in
separate transaction with a reverse-path of <>.
<<< 220-Bombs.AF.MIL reporting for duty
<<< 220 Electronic mail is to be used for official business only
>>> EHLO Pure-Heart.
<<< 502 command not
>>>
<<< 250
>>> HELO Pure-Heart.
<<< 250 Bombs.AF.
>>> MAIL FROM:
<<< 250
>>> RCPT TO:
<<< 250
>>>
<<< 354 send
>>> (message goes here
>>> .
<<< 250 message
>>> MAIL FROM:<>
<<< 250
Moore Standards Track [Page 25]
RFC 1891 SMTP Delivery Status Notifications January 1996
>>> RCPT TO:
<<< 250
>>>
<<< 354 send
>>> (message goes here
>>> .
<<< 250 message
>>>
<<< 221 Bombs.AF.MIL closing
10.5 Forward from George@Tax-ME.GOV to Sam@Boondoggle.
The SMTP at Pure-Heart.ORG relays the message to Tax-ME.GOV. (
step is not shown). MTA Tax-ME.GOV then forwards the message
Sam@Boondoggle.GOV (shown below). Both Tax-ME.GOV and Pure-Heart.
support the SMTP DSN extension. Note that RET, ENVID, and ORCPT
retain their original values
<<< 220 BoonDoggle.GOV says
>>> EHLO Pure-Heart.
<<< 250-mail.Big-Bucks.
<<< 250
>>> MAIL FROM: RET=HDRS ENVID=QQ314159
<<< 250 sender
>>> RCPT TO: NOTIFY=SUCCESS \
ORCPT=rfc822;George@Tax-ME.
<<< 250 recipient
>>>
<<< 354 send
>>> (message goes here
>>> .
<<< 250 message
>>>
<<< 221
Moore Standards Track [Page 26]
RFC 1891 SMTP Delivery Status Notifications January 1996
10.6 "Delivered" DSN for Bob@Big-Bucks.
MTA mail.Big-Bucks.COM successfully delivers the message to Bob@Big
Bucks.COM. Because the sender specified NOTIFY=SUCCESS, mail.Big
Bucks.COM issues the following DSN, and sends it to Alice@Pure
Heart.ORG
To: Alice@Pure-Heart.
From: postmaster@mail.Big-Bucks.
Subject: Delivery Notification (success) for Bob@Big-Bucks.
Content-Type: multipart/report; report-type=delivery-status
boundary=
MIME-Version: 1.0
--
Content-type: text/plain; charset=us-
Your message (id QQ314159) was successfully delivered
Bob@Big-Bucks.COM
--
Content-type: message/delivery-
Reporting-MTA: dns; mail.Big-Bucks.
Original-Envelope-ID: QQ314159
Original-Recipient: rfc822;Bob@Big-Bucks.
Final-Recipient: rfc822;Bob@Big-Bucks.
Action:
Status: 2.0.0
--
Content-type: message/rfc822
(headers of returned message go here
--abcde--
Moore Standards Track [Page 27]
RFC 1891 SMTP Delivery Status Notifications January 1996
10.7 Failed DSN for Carol@Ivory.
Because delivery to Carol failed and the sender
NOTIFY=FAILURE for Carol@Ivory.EDU, MTA Pure-Heart.ORG (the
client to which the failure was reported via SMTP) issues
following DSN
To: Alice@Pure-Heart.
From: postmaster@Pure-Heart.
Subject: Delivery Notification (failure) for Carol@Ivory.
Content-Type: multipart/report; report-type=delivery-status
boundary=
MIME-Version: 1.0
--
Content-type: text/plain; charset=us-
Your message (id QQ314159) could not be delivered
Carol@Ivory.EDU
A transcript of the session follows
(while talking to Ivory.EDU
>>> RCPT TO: NOTIFY=
<<< 550 error - no such
--
Content-type: message/delivery-
Reporting-MTA: dns; Pure-Heart.
Original-Envelope-ID: QQ314159
Original-Recipient: rfc822;Carol@Ivory.
Final-Recipient: rfc822;Carol@Ivory.
SMTP-Remote-Recipient: Carol@Ivory.
Diagnostic-Code: smtp; 550 error - no such
Action:
Status: 5.0.0
--
Content-type: message/rfc822
(headers of returned message go here
--bcdef--
Moore Standards Track [Page 28]
RFC 1891 SMTP Delivery Status Notifications January 1996
10.8 Relayed DSN For Dana@Ivory.
Although the mail gateway Ivory.EDU supports the DSN SMTP extension
the LAN mail system attached to its other side does not
positive delivery confirmations. So Ivory.EDU issues a "relayed
DSN
To: Alice@Pure-Heart.
From: postmaster@Ivory.
Subject: mail relayed for Dana@Ivory.
Content-Type: multipart/report; report-type=delivery-status
boundary=
MIME-Version: 1.0
--
Content-type: text/plain; charset=us-
Your message (addressed to Dana@Ivory.EDU) was
relayed to
ymail!
by the FooMail gateway at Ivory.EDU
Unfortunately, the remote mail system does not
confirmation of actual delivery. Unless delivery to ymail!
fails, this will be the only delivery status notification sent
--
Content-type: message/delivery-
Reporting-MTA: dns; Ivory.
Original-Envelope-ID: QQ314159
Original-Recipient: rfc822;Dana@Ivory.
Final-Recipient: rfc822;Dana@Ivory.
Action:
Status: 2.0.0
--
Content-type: message/rfc822
(headers of returned message go here
--cdefg--
Moore Standards Track [Page 29]
RFC 1891 SMTP Delivery Status Notifications January 1996
10.9 Failure notification for Sam@Boondoggle.
The message originally addressed to George@Tax-ME.GOV was
to Sam@Boondoggle.GOV, but the MTA for Boondoggle.GOV was unable
deliver the message due to a lack of disk space in Sam's mailbox
After trying for several days, Boondoggle.GOV returned the
DSN
To: Alice@BigHeart.
From: Postmaster@Boondoggle.
Subject: Delivery failure for Sam@Boondoggle.
Content-Type: multipart/report; report-type=delivery-status
boundary=
MIME-Version: 1.0
--
Your message, originally addressed to George@Tax-ME.GOV, and
from there to Sam@Boondoggle.GOV could not be delivered, for
following reason
write error to mailbox, disk quota
--
Content-type: message/delivery-
Reporting-MTA: Boondoggle.
Original-Envelope-ID: QQ314159
Original-Recipient: rfc822;George@Tax-ME.
Final-Recipient: rfc822;Sam@Boondoggle.
Action:
Status: 4.2.2 (disk quota exceeded
--
Content-type: message/rfc822
(headers of returned message go here
--defgh--
Moore Standards Track [Page 30]
RFC 1891 SMTP Delivery Status Notifications January 1996
11.
[1] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
USC/Information Sciences Institute, August 1982.
[2] Crocker, D., "Standard for the Format of ARPA Internet
Messages", STD 11, RFC 822, UDEL, August 1982.
[3] Westine, A., and J. Postel, "Problems with the Maintenance
Large Mailing Lists.", RFC 1211, USC/Information
Institute, March 1991.
[4] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D. Crocker
"SMTP Service Extensions", RFC 1651, MCI, Innosoft, Dover
Consulting, Inc., Network Management Associates, Inc.,
Graphics, Inc., July 1994.
[5] Moore, K., and G. Vaudreuil, "An 