SMTP 521 and 556 Reply Codes
RFC 7504
| Document | Type |
RFC - Proposed Standard
(June 2015; No errata)
Was draft-klensin-smtp-521code (individual in app area)
|
|
|---|---|---|---|
| Last updated | 2015-10-14 | ||
| Replaces | draft-klensin-rfc1846bis | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| Stream | WG state | (None) | |
| Document shepherd | Tony Hansen | ||
| Shepherd write-up | Show (last changed 2015-03-05) | ||
| IESG | IESG state | RFC 7504 (Proposed Standard) | |
| Consensus Boilerplate | Yes | ||
| Telechat date | |||
| Responsible AD | Barry Leiba | ||
| Send notices to | ietf-smtp@ietf.org | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA action state | RFC-Ed-Ack | ||
Internet Engineering Task Force (IETF) J. Klensin
Request for Comments: 7504 June 2015
Updates: 1846, 5321
Category: Standards Track
ISSN: 2070-1721
SMTP 521 and 556 Reply Codes
Abstract
This memo defines two Simple Mail Transfer Protocol (SMTP) reply
codes, 521 and 556. The 521 code was originally described in an
Experimental RFC in 1995 and is in wide use, but has not previously
been formally incorporated into SMTP. The 556 code was created to
support the new tests and actions specified in RFC 7505. These codes
are used to indicate that an Internet host does not accept incoming
mail at all. This specification is not applicable when the host
sometimes accepts mail but may reject particular messages, or even
all messages, under specific circumstances.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7504.
Klensin Standards Track [Page 1]
RFC 7504 SMTP 521 and 556 Reply Codes June 2015
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. The 521 Reply Code . . . . . . . . . . . . . . . . . . . . . 4
4. The 556 Reply Code . . . . . . . . . . . . . . . . . . . . . 4
5. Small Details to Avoid Loose Ends . . . . . . . . . . . . . . 5
5.1. Specific Changes to RFC 5321 . . . . . . . . . . . . . . 5
5.2. The RFC 1846 Experiment . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
Klensin Standards Track [Page 2]
RFC 7504 SMTP 521 and 556 Reply Codes June 2015
1. Introduction
The SMTP specification [2] (referred to, along with its various
updates, as "SMTP" below) contains a list and discussion of reply
codes. This document updates that list with a new code, 521, for use
in response to an initial connection. In that context, it
specifically denotes a system that does not receive mail or otherwise
handle SMTP mail or inquiry transactions. That code differs from the
use of reply code 554, recommended by RFC 5321, because the latter
code can be used in a larger variety of situations, including mail
that is not accepted for, or from, particular sources, destinations,
or addresses. It also introduces a second reply code, 556, for use
when an SMTP client encounters a domain in a forward-pointing address
that it can determine (e.g., from the DNS "null MX" convention [5])
does not support receipt of mail and has to report that condition to
a host that delivered the message to it for further processing.
This specification updates RFC 5321 to add the new codes. The 521
code was first formally proposed in the Experimental RFC 1846 [4];
this document updates that specification to standardize the code and
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