Network Working Group A. Melnikov
Internet-Draft Isode Ltd
Intended status: Standards Track 13 May 2025
Expires: 14 November 2025
Updates to SMTP related IANA registries
draft-melnikov-smtp-iana-cleanup-01
Abstract
While EMAILCORE working group was working on update to SMTP
specification, it became clear that existing entries in SMTP related
registries are missing information or contain stale information and
need to be updated. This document updates such entries.
Status of This Memo
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This Internet-Draft will expire on 14 November 2025.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 2
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 2
3.1. Updates to the "Simple Mail Transfer Protocol (SMTP)
Service Extensions" registry . . . . . . . . . . . . . . 3
3.1.1. Updates to the "References" field . . . . . . . . . . 3
3.1.2. Updates to the "EHLO Parameters" field . . . . . . . 3
3.1.3. Updates to the "Message submission Use and Values"
field . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1.4. Updates to the "Additional verbs", "MAIL/RCPT Parameter
Values" fields . . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Normative References . . . . . . . . . . . . . . . . . . 8
5.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
While EMAILCORE working group was working on update to SMTP
specification [I-D.ietf-emailcore-rfc5321bis], it became clear that
existing entries in SMTP related registries are missing information
or contain stale information and need to be updated. This document
updates such entries, assuming IANA actions specified in
[I-D.ietf-emailcore-rfc5321bis] were already performed.
This document doesn't do any restructuring to existing SMTP related
entries.
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. IANA Considerations
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3.1. Updates to the "Simple Mail Transfer Protocol (SMTP) Service
Extensions" registry
Updates to the "Simple Mail Transfer Protocol (SMTP) Service
Extensions" registry are described as an ordered list of steps that
should be performed sequentually. Each step is described by a
subsection of this section.
3.1.1. Updates to the "References" field
IANA is requested to change values of the "References" field for
"EXPN" and "HELP" extensions to [I-D.ietf-emailcore-rfc5321bis]. The
"References" field values for "SEND", "SOML", "SAML" and "TURN"
remain unchanged, as they were obsoleted and there are no newer
reference than RFC 821.
3.1.2. Updates to the "EHLO Parameters" field
IANA is requested to update the following values in this field:
1. The value corresponding to the DELIVERBY extension should be
changed to "A comma separated list of options (optional)", as per
[RFC2852].
2. The value corresponding to the FUTURERELEASE extension should be
changed to "max-future-release-interval and max-future-release-
date-time", as per [RFC4865].
3. The value corresponding to the LIMITS extension should be changed
to "List of limits", as per [RFC9422].
3.1.3. Updates to the "Message submission Use and Values" field
IANA is requested to update values of the "Message submission Use and
Values" field corresponding to "HELP", "BURL", "FUTURERELEASE",
"SMTPUTF8", "MT-PRIORITY", "RRVS", "REQUIRETLS" and "LIMITS"
extensions to "MAY".
3.1.4. Updates to the "Additional verbs", "MAIL/RCPT Parameter Values"
fields
IANA is requested to update "Additional verbs" and "MAIL/RCPT
Parameter Values" fields as per the table specified below.
Information for relevant fields was extracted from existing RFCs
describing corresponding SMTP Extensions.
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+=====================+============+================================+
| EHLO Keyword | Additional | MAIL/RCPT Parameter Values |
| | verbs | |
+=====================+============+================================+
| SEND | SEND | none |
+---------------------+------------+--------------------------------+
| SOML | SOML | none |
+---------------------+------------+--------------------------------+
| SAML | SAML | none |
+---------------------+------------+--------------------------------+
| EXPN | EXPN | none |
+---------------------+------------+--------------------------------+
| HELP | HELP | none |
+---------------------+------------+--------------------------------+
| TURN | TURN | none |
+---------------------+------------+--------------------------------+
| 8BITMIME | none | BODY parameter to MAIL |
| | | command |
+---------------------+------------+--------------------------------+
| SIZE | none | SIZE parameter to MAIL |
| | | command |
+---------------------+------------+--------------------------------+
| CHUNKING | BDAT | none |
+---------------------+------------+--------------------------------+
| BINARYMIME | none | BODY parameter to MAIL |
| | | command (an extra choice |
| | | was added) |
+---------------------+------------+--------------------------------+
| CHECKPOINT | none | TRANSID parameter to the |
| | | MAIL command |
+---------------------+------------+--------------------------------+
| DELIVERBY | none | BY parameter to MAIL |
| | | command |
+---------------------+------------+--------------------------------+
| PIPELINING | none | none |
+---------------------+------------+--------------------------------+
| DSN | none | NOTIFY and ORCPT |
| | | parameters to RCPT |
| | | command. RET and ENVID |
| | | parameters to MAIL command |
+---------------------+------------+--------------------------------+
| ETRN | ETRN | none |
+---------------------+------------+--------------------------------+
| ENHANCEDSTATUSCODES | none | none |
+---------------------+------------+--------------------------------+
| STARTTLS | STARTTLS | none |
+---------------------+------------+--------------------------------+
| NO-SOLICITING | none | SOLICIT parameter to MAIL |
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| | | command |
+---------------------+------------+--------------------------------+
| MTRK | none | MTRK parameters to MAIL |
| | | command. Also see DSN |
| | | extension parameters |
+---------------------+------------+--------------------------------+
| SUBMITTER | none | SUBMITTER parameters to |
| | | MAIL command |
+---------------------+------------+--------------------------------+
| ATRN | ATRN | none |
+---------------------+------------+--------------------------------+
| AUTH | AUTH | AUTH parameter to MAIL |
| | | command |
+---------------------+------------+--------------------------------+
| BURL | BURL | none |
+---------------------+------------+--------------------------------+
| FUTURERELEASE | none | HOLDFOR and HOLDUNTIL |
| | | parameters to MAIL |
| | | command. |
+---------------------+------------+--------------------------------+
| UTF8SMTP | none | One optional parameter, |
| | | ALT-ADDRESS, is added to |
| | | the MAIL and RCPT commands |
+---------------------+------------+--------------------------------+
| CONPERM | none | CONPERM parameter to MAIL |
| | | command |
+---------------------+------------+--------------------------------+
| CONNEG | none | CONNEG parameter to RCPT |
| | | command |
+---------------------+------------+--------------------------------+
| SMTPUTF8 | none | SMTPUTF8 parameter to the |
| | | MAIL command |
+---------------------+------------+--------------------------------+
| MT-PRIORITY | none | MT-PRIORITY parameter to |
| | | MAIL command |
+---------------------+------------+--------------------------------+
| RRVS | none | RRVS parameter to RCPT |
| | | command |
+---------------------+------------+--------------------------------+
| REQUIRETLS | none | REQUIRETLS parameter to |
| | | MAIL command |
+---------------------+------------+--------------------------------+
| LIMITS | none | none |
+---------------------+------------+--------------------------------+
Table 1
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IANA is further requested to update "Length Added" fields as per the
table specified below. Information for this field was either
extracted or calculated from information in existing RFCs describing
corresponding SMTP Extensions.
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+===============+========+========================================+
| EHLO Keyword | Length | Comment |
| | Added | |
+===============+========+========================================+
| SIZE | 26 | https://datatracker.ietf.org/doc/html/ |
| | | rfc1870#section-3 |
+---------------+--------+----------------------------------------+
| CHUNKING | 0 | https://datatracker.ietf.org/doc/html/ |
| | | rfc3030#section-2 |
+---------------+--------+----------------------------------------+
| BINARYMIME | 16 | https://datatracker.ietf.org/doc/html/ |
| | | rfc3030#section-3 |
+---------------+--------+----------------------------------------+
| CHECKPOINT | 88 | https://datatracker.ietf.org/doc/html/ |
| | | rfc1845#section-2 |
+---------------+--------+----------------------------------------+
| DELIVERBY | 17 | https://datatracker.ietf.org/doc/html/ |
| | | rfc2852#section-2 |
+---------------+--------+----------------------------------------+
| MTRK | 40 | https://datatracker.ietf.org/doc/html/ |
| | | rfc3885#section-2 |
+---------------+--------+----------------------------------------+
| AUTH | 500 | https://datatracker.ietf.org/doc/html/ |
| | | rfc4954#section-3 |
+---------------+--------+----------------------------------------+
| FUTURERELEASE | 34 | https://datatracker.ietf.org/doc/html/ |
| | | rfc4865#section-3 |
+---------------+--------+----------------------------------------+
| UTF8SMTP | 460 | https://datatracker.ietf.org/doc/html/ |
| | | rfc5336#section-3.1 |
+---------------+--------+----------------------------------------+
| SMTPUTF8 | 10 | https://datatracker.ietf.org/doc/html/ |
| | | rfc6531#section-3.1 |
+---------------+--------+----------------------------------------+
| MT-PRIORITY | 15 | https://datatracker.ietf.org/doc/html/ |
| | | rfc6710#section-3 |
+---------------+--------+----------------------------------------+
| RRVS | 33 | https://datatracker.ietf.org/doc/html/ |
| | | rfc7293#section-3.1 |
+---------------+--------+----------------------------------------+
| REQUIRETLS | 11 | https://www.rfc-editor.org/rfc/ |
| | | rfc8689.html#name-iana-considerations |
+---------------+--------+----------------------------------------+
Table 2
TBD: Calculate "Length Added" when not specified in existing RFCs.
Also possibly merge this with the previous table?
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4. Security Considerations
This document only specifies IANA related actions, thus it doesn't
directly affect security on SMTP or its extensions. However better
documentation of SMTP extensions in IANA registries can, hopefully,
lead to better and more secure implementations.
5. References
5.1. Normative References
[I-D.ietf-emailcore-rfc5321bis]
Klensin, J. C., "Simple Mail Transfer Protocol", Work in
Progress, Internet-Draft, draft-ietf-emailcore-rfc5321bis-
43, 28 April 2025, <https://datatracker.ietf.org/doc/html/
draft-ietf-emailcore-rfc5321bis-43>.
[RFC1845] Crocker, D., Freed, N., and A. Cargille, "SMTP Service
Extension for Checkpoint/Restart", RFC 1845,
DOI 10.17487/RFC1845, September 1995,
<https://www.rfc-editor.org/info/rfc1845>.
[RFC1870] Klensin, J., Freed, N., and K. Moore, "SMTP Service
Extension for Message Size Declaration", STD 10, RFC 1870,
DOI 10.17487/RFC1870, November 1995,
<https://www.rfc-editor.org/info/rfc1870>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2852] Newman, D., "Deliver By SMTP Service Extension", RFC 2852,
DOI 10.17487/RFC2852, June 2000,
<https://www.rfc-editor.org/info/rfc2852>.
[RFC3030] Vaudreuil, G., "SMTP Service Extensions for Transmission
of Large and Binary MIME Messages", RFC 3030,
DOI 10.17487/RFC3030, December 2000,
<https://www.rfc-editor.org/info/rfc3030>.
[RFC3885] Allman, E. and T. Hansen, "SMTP Service Extension for
Message Tracking", RFC 3885, DOI 10.17487/RFC3885,
September 2004, <https://www.rfc-editor.org/info/rfc3885>.
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[RFC4865] White, G. and G. Vaudreuil, "SMTP Submission Service
Extension for Future Message Release", RFC 4865,
DOI 10.17487/RFC4865, May 2007,
<https://www.rfc-editor.org/info/rfc4865>.
[RFC5336] Yao, J., Ed. and W. Mao, Ed., "SMTP Extension for
Internationalized Email Addresses", RFC 5336,
DOI 10.17487/RFC5336, September 2008,
<https://www.rfc-editor.org/info/rfc5336>.
[RFC6409] Gellens, R. and J. Klensin, "Message Submission for Mail",
STD 72, RFC 6409, DOI 10.17487/RFC6409, November 2011,
<https://www.rfc-editor.org/info/rfc6409>.
[RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized
Email", RFC 6531, DOI 10.17487/RFC6531, February 2012,
<https://www.rfc-editor.org/info/rfc6531>.
[RFC6710] Melnikov, A. and K. Carlberg, "Simple Mail Transfer
Protocol Extension for Message Transfer Priorities",
RFC 6710, DOI 10.17487/RFC6710, August 2012,
<https://www.rfc-editor.org/info/rfc6710>.
[RFC7293] Mills, W. and M. Kucherawy, "The Require-Recipient-Valid-
Since Header Field and SMTP Service Extension", RFC 7293,
DOI 10.17487/RFC7293, July 2014,
<https://www.rfc-editor.org/info/rfc7293>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8689] Fenton, J., "SMTP Require TLS Option", RFC 8689,
DOI 10.17487/RFC8689, November 2019,
<https://www.rfc-editor.org/info/rfc8689>.
[RFC9422] Freed, N. and J. Klensin, "The LIMITS SMTP Service
Extension", RFC 9422, DOI 10.17487/RFC9422, February 2024,
<https://www.rfc-editor.org/info/rfc9422>.
5.2. Informative References
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
DOI 10.17487/RFC5321, October 2008,
<https://www.rfc-editor.org/info/rfc5321>.
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Appendix A. Acknowledgements
Thank you to John Klensin and Tero Kivinen for suggestions, comments
and corrections on this document.
Tero Kivinen provided initial version of the table with Length Added
values for various SMTP extensions.
Author's Address
Alexey Melnikov
Isode Ltd
14 Castle Mews
Hampton
TW12 2NP
United Kingdom
Email: alexey.melnikov@isode.com
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