The LIMITS SMTP Service Extension
draft-freed-smtp-limits-07

Received changes through RFC Editor sync (changed state to RFC, created became rfc relationship between draft-freed-smtp-limits and RFC 9422, changed IESG state to RFC Published)

[Ballot comment]
** Section 6.  Editorial.  In the spirit of inclusive language consider s/A man-in-the-middle attack/An on-path attack/

** Section 6.
  All that said, decades of operational experience with the SMTP "SIZE"
  extension [SIZE], which provides servers with the ability to indicate
  message size, indicates that such abuse is rare and unlikely to be a
  significant problem.

Consider adding that opportunistic encryption/STARTTLS would also help mitigate on-path tampering of these values.

[Ballot comment]
I see that SIZE was a "limit" handled previously in RFC1870. However, when reading that limit, I don't see any language as present in this document about new SIZE limits after authentication. Is that something appropriate to add to this document? I don't see another document that updates 1870 for this?

Would it make sense to also fold in SIZE into this new limit syntax in the hopes of perhaps obsoleting the SIZE extension as a separate extension a decade from now ?

[Ballot comment]
I see that SIZE was a "limit" handled previously in RFC1870. However, when reading that limit, I don't see any language as present in this document about new SIZE limits after authentication. Is that something appropriate to add to this document? I don't see another document that updates 1870 for this?

Would it make size to also fold in SIZE into this new limit syntax in the hopes of perhaps obsoleting the SIZE extension as a separate extension a decade from now ?

[Ballot comment]
John, thank you for shepherding Ned's document through to RFC.

I have one very minor nit, which is a typo on 'Regisry' in section 7.1.

Regards,
Rob

(Via drafts-lastcall@iana.org): IESG/Authors/WG Chairs:

IANA has completed its review of draft-freed-smtp-limits-06. If any part of this review is inaccurate, please let us know.

IANA has a question and a note about the second action requested in the document's IANA Considerations section.

We understand that upon approval of this document, there are two actions to complete:

First, in the SMTP Service Extensions registry in the MAIL Parameters registry group at

https://www.iana.org/assignments/mail-parameters/

a single new registration will be made:

EHLO Keyword: LIMITS
Description: Server limits
Reference: [ RFC-to-be ]
Note:

Second, a new registry called the SMTP Server Limits registry will be created.

QUESTION:

Where should this new registry be located? Should it be added to an existing registry group (i.e. a collection of registries at one URL, like "MAIL Parameters")? If it needs a new group, does it also need a new category at http://www.iana.org/protocols (and if so, should the group and the category have the same name)?

The new registry will be managed via Specification Required, as defined by RFC 8126 (but please see the IANA note below for further considerations for the management of the registry).

NOTE:

Section 7.2 states that the registration procedure proposed in draft-klensin-iana-consid-hybrid could be used if that option becomes available and generally accepted. However, authors are not required to use registration procedures defined in RFC 8126. The author could describe it and use it in this document.

If so, we would suggest that the procedure be separated into something like "IETF Review (Standards Track or Experimental Preferred)" and First Come First Served.

Also, if the hybrid document is proposing a procedure that provides those two options, it isn't clear why the latter isn't being proposed as a second registration procedure when this document goes on to say that Specification Required should be used if the hybrid procedure can't be. Registries at https://www.iana.org/assignments/quic and https://www.iana.org/assignments/uri-schemes allow for "provisional" registrations made via FCFS and "permanent" registrations made via another procedure. The specific terms "provisional" and "permanent" aren't required if they aren't appropriate, but even if the hybrid procedure were used, the registry would presumably have to provide some set of labels in the registry that would be used to distinguish registrations made via FCFS from registrations that required a particular kind of RFC and/or an expert review.

There are three initial registrations in the new registry:

Name: MAILMAX
Value syntax: %x31-39 0*5DIGIT ; 0 not allowed, 6 digit maximum
Description: MAILMAX specifies the maximum number of transactions (MAIL FROM commands) the server will accept in a single session. The count includes all MAIL FROM commands, regardless of whether they succeed or fail.
Restrictions: None.
Security Considerations: See [ RFC-to-be, Section 6]
Reference: [ RFC-to-be ]

Name: RCPTMAX
Value syntax: %x31-39 0*5DIGIT ; 0 not allowed, 6 digit maximum
Description: RCPTMAX specifies the maximum number of RCPT TO commands the server will accept in a single transaction. It is not a limit on the actual number of recipients the message ends up being sent to; a single RCPT TO command may produce multiple recipients or, in the event of an error, none.
Restrictions: None.
Security Considerations: See [ RFC-to-be, Section 6]
Reference: [ RFC-to-be ]

Name: RCPTDOMAINMAX
Value syntax: %x31-39 0*5DIGIT ; 0 not allowed, 6 digit maximum
Description: RCPTDOMAINMAX specifies the maximum number of different domains that can appear in a recipient (RCPT TO) address within a single session. This limit is imposed by some servers that bind to a specific internal delivery mechanism on receipt of the first RCPT TO command.
Restrictions: None.
Security Considerations: See [ RFC-to-be, Section 6]
Reference: [ RFC-to-be ]

IANA understands that these are the only two IANA actions required by the document.

For definitions of IANA review states, please see:

https://datatracker.ietf.org/help/state/draft/iana-review

Thank you,

Amanda Baber
IANA Operations Manager

The following Last Call announcement was sent out (ends 2023-10-04):

From: The IESG
To: IETF-Announce
CC: draft-freed-smtp-limits@ietf.org, superuser@gmail.com
Reply-To: last-call@ietf.org
Sender:
Subject: Last Call:  (The LIMITS SMTP Service Extension) to Proposed Standard


The IESG has received a request from an individual submitter to consider the
following document: - 'The LIMITS SMTP Service Extension'
  as Proposed Standard

The IESG plans to make a decision in the next few weeks, and solicits final
comments on this action. Please send substantive comments to the
last-call@ietf.org mailing lists by 2023-10-04. Exceptionally, comments may
be sent to iesg@ietf.org instead. In either case, please retain the beginning
of the Subject line to allow automated sorting.

Abstract


  This document defines a "Limits" extension for the Simple Mail
  Transfer Protocol (SMTP), including submission, as well as the Local
  Mail Transfer Protocol (LMTP).  It also defines an associated limit
  registry.  The extension provides the means for an SMTP, submission,
  or LMTP server to inform the client of limits the server intends to
  apply to the protocol during the current session.  The client is then
  able to adapt its behavior in order to conform to those limits.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-freed-smtp-limits/



No IPR declarations have been submitted directly on this I-D.

# Document Shepherd Write-Up for Individual Documents

*This version is dated 4 July 2022.*

Thank you for your service as a document shepherd. Among the responsibilities is
answering the questions in this write-up to give helpful context to Last Call
and Internet Engineering Steering Group ([IESG][1]) reviewers, and your
diligence in completing it is appreciated. The full role of the shepherd is
further described in [RFC 4858][2]. You will need the cooperation of the authors
and editors to complete these checks.

Note that some numbered items contain multiple related questions; please be sure
to answer all of them.

## Document History

1. Was the document considered in any WG, and if so, why was it not adopted as a
  work item there?

It was considered in EMAILCORE, which chose not to process it.  As there is no other appropriate home for it in the ART area at this time, it is now a sponsored document.

2. Was there controversy about particular points that caused the WG to not adopt
  the document?

Only its charter.  The work otherwise got good discussion followed by general supportive grumbling from the appropriate community.

3. Has anyone threatened an appeal or otherwise indicated extreme discontent? If
  so, please summarize the areas of conflict in separate email messages to the
  responsible Area Director. (It should be in a separate email because this
  questionnaire is publicly available.)

No.

4. For protocol documents, are there existing implementations of the contents of
  the document? Have a significant number of potential implementers indicated
  plans to implement? Are any existing implementations reported somewhere,
  either in the document itself (as [RFC 7942][3] recommends) or elsewhere
  (where)?

(inquiry pending)

## Additional Reviews

5. Do the contents of this document closely interact with technologies in other
  IETF working groups or external organizations, and would it therefore benefit
  from their review? Have those reviews occurred? If yes, describe which
  reviews took place.

Other than EMAILCORE (see above), no.  It might be beneficial to make M3AAWG aware of it, but that's probably a unidirectional communication.

6. Describe how the document meets any required formal expert review criteria,
  such as the MIB Doctor, YANG Doctor, media type, and URI type reviews.

None required.

7. If the document contains a YANG module, has the final version of the module
  been checked with any of the [recommended validation tools][4] for syntax and
  formatting validation? If there are any resulting errors or warnings, what is
  the justification for not fixing them at this time? Does the YANG module
  comply with the Network Management Datastore Architecture (NMDA) as specified
  in [RFC 8342][5]?

No YANG here.

8. Describe reviews and automated checks performed to validate sections of the
  final version of the document written in a formal language, such as XML code,
  BNF rules, MIB definitions, CBOR's CDDL, etc.

ABNF is relatively simple, and was reviewed manually.

## Document Shepherd Checks

9. Based on the shepherd's review of the document, is it their opinion that this
  document is needed, clearly written, complete, correctly designed, and ready
  to be handed off to the responsible Area Director?

Yes.

10. Several IETF Areas have assembled [lists of common issues that their
    reviewers encounter][6]. For which areas have such issues been identified
    and addressed? For which does this still need to happen in subsequent
    reviews?

The appropriate ART area reviews have occurred.

11. What type of RFC publication is being requested on the IETF stream ([Best
    Current Practice][12], [Proposed Standard, Internet Standard][13],
    [Informational, Experimental or Historic][14])? Why is this the proper type
    of RFC? Do all Datatracker state attributes correctly reflect this intent?

Proposed Standard is sought.  This is appropriate given it describes an extension to SMTP which is a Draft Standard.  The front page and all the usual places reflect this.

12. Have reasonable efforts been made to remind all authors of the intellectual
    property rights (IPR) disclosure obligations described in [BCP 79][7]? To
    the best of your knowledge, have all required disclosures been filed? If
    not, explain why. If yes, summarize any relevant discussion, including links
    to publicly-available messages when applicable.

Yes, all one of them has been reminded.  No disclosures have been filed, and none are anticipated.

13. Has each author, editor, and contributor shown their willingness to be
    listed as such? If the total number of authors and editors on the front page
    is greater than five, please provide a justification.

Yes.

14. Document any remaining I-D nits in this document. Simply running the [idnits
    tool][8] is not enough; please review the ["Content Guidelines" on
    authors.ietf.org][15]. (Also note that the current idnits tool generates
    some incorrect warnings; a rewrite is underway.)

No nits were reported when the current version was posted.

15. Should any informative references be normative or vice-versa? See the [IESG
    Statement on Normative and Informative References][16].

No, they look right to me.

16. List any normative references that are not freely available to anyone. Did
    the community have sufficient access to review any such normative
    references?

None.

17. Are there any normative downward references (see [RFC 3967][9] and [BCP
    97][10]) that are not already listed in the [DOWNREF registry][17]? If so,
    list them.

No.

18. Are there normative references to documents that are not ready to be
    submitted to the IESG for publication or are otherwise in an unclear state?
    If so, what is the plan for their completion?

No, although it is possible an anticipated revision to RFC 8126bis may generate a revision to the registration policies of the registry created here.  There's no other process to do so apart from blocking this until that publishes, but that could be a long time.

19. Will publication of this document change the status of any existing RFCs? If
    so, does the Datatracker metadata correctly reflect this and are those RFCs
    listed on the title page, in the abstract, and discussed in the
    introduction? If not, explain why and point to the part of the document
    where the relationship of this document to these other RFCs is discussed.

No.

20. Describe the document shepherd's review of the IANA considerations section,
    especially with regard to its consistency with the body of the document.
    Confirm that all aspects of the document requiring IANA assignments are
    associated with the appropriate reservations in IANA registries. Confirm
    that any referenced IANA registries have been clearly identified. Confirm
    that each newly created IANA registry specifies its initial contents,
    allocations procedures, and a reasonable name (see [RFC 8126][11]).

The IANA Considerations section appears to be correct and complete.  It creates a "Specification Required" registry, and RFC 8126 says such an action SHOULD be accompanied by advice to the Designated Expert(s).  Such should be added before this goes to publication.

21. List any new IANA registries that require Designated Expert Review for
    future allocations. Are the instructions to the Designated Expert clear?
    Please include suggestions of designated experts, if appropriate.

See above.

[1]: https://www.ietf.org/about/groups/iesg/
[2]: https://www.rfc-editor.org/rfc/rfc4858.html
[3]: https://www.rfc-editor.org/rfc/rfc7942.html
[4]: https://wiki.ietf.org/group/ops/yang-review-tools
[5]: https://www.rfc-editor.org/rfc/rfc8342.html
[6]: https://wiki.ietf.org/group/iesg/ExpertTopics
[7]: https://www.rfc-editor.org/info/bcp79
[8]: https://www.ietf.org/tools/idnits/
[9]: https://www.rfc-editor.org/rfc/rfc3967.html
[10]: https://www.rfc-editor.org/info/bcp97
[11]: https://www.rfc-editor.org/rfc/rfc8126.html
[12]: https://www.rfc-editor.org/rfc/rfc2026.html#section-5
[13]: https://www.rfc-editor.org/rfc/rfc2026.html#section-4.1
[14]: https://www.rfc-editor.org/rfc/rfc2026.html#section-4.2
[15]: https://authors.ietf.org/en/content-guidelines-overview
[16]: https://www.ietf.org/about/groups/iesg/statements/normative-informative-references/
[17]: https://datatracker.ietf.org/doc/downref/