Tunneling of SMTP Message Transfer Priorities
draft-melnikov-smtp-priority-tunneling-04

[Ballot comment]
The IESG is fine with moving this to Informational, and that satisfies my concerns. I will work with the author to get this made into Informational.

[Ballot discuss]
Between Adrian's comment and Barry's, I am no longer convinced that Experimental is the correct status for this document (and I kick myself for not noticing this earlier on my own). I'm considering Informational. I'd like to discuss this issue, and not only with myself.

[Ballot comment]
I have no objection to the publication of this document, and welcome that it is Experimental.

As with many Experimental documents I review, I would like the Abstract to note the Experimental status (as, for example, is done in the first line of the Introduction). I should also like to see a little more scoping of the Experiment:
- why it is experimental
- what nodes participate in the experiment
- how the experiment is constrained
- how the experiment will be judged

It is not mandatory to add such text (hence this is not a Discuss), but I think it really helps people work out how to work with the document.

[Ballot discuss]

  Based on the discussion following the posting of the Gen-ART Review
  by Martin Thomson on 8-June-2012, it seems that there is an
  inconsistency that needs to be resolved:
  >
  > But now that I am looking at the two sections ("Security
  > Considerations" and "Relay of messages to non-conforming SMTP
  > servers"), they might be out of sync as far as requirements are
  > concerned. So I need to tweak one or both of them to match.

[Ballot comment]
INTRODUCTION, paragraph 4:

>    This memo defines a mechanism for tunneling of SMTP (Simple Mail
>    Transfer Protocol) Message Transfer Priority values through MTAs
>    (Message Transfer Agents) that don't support the MT-PRIORITY SMTP
>    extension.

  Shouldn't this hint to the fact that this memo is updating
  [SMTP-PRIORITY], as stated in Section 3.1 and the following sections?

[Ballot comment]


- Section 7, 1st para: How would one use S/MIME to sign the
MT-Priority header field? You'd have to encapsulate the message
wouldn't you? I think you could omit mention of S/MIME here.

- Section 7, 1st para (again:-): DKIM doesn't allow you to know
who put this header on, just who signed it (if its included in
the signature). So I think what you want to say is something
like "DKIM signing allows a recipient to verify that the
specified priority value was present when the message was
signed, and to verify who signed the message." But the signer
might not be the one that "generated" the header.

- Same section: Calling for an MUA to use DKIM is a bit of a
stretch, but would I guess work, though the key mgmt isn't very
well-defined for that use-case really since you end up with
per-user keys in the DNS, or have to share private keys.

[Ballot comment]
As I noted in the shepherd writeup, I have some concern about the broader applicability of this as a standard, given the trade-offs the proponents have made.  That said, some of them had to be made, and there is value in implementing features from proprietary email systems in standardized ways on the open Internet.  There does seem to be consensus that it's worth trying this out, and that it's not terribly unsafe to do so.

The tunneling of the PRIORITY value through non-conforming MTAs by turning it into a message header field (MT-Priority) and then back again is a problematic technique, but is an important capability for those who need and intend to implement the smtp-priority extension.  It creates a trust issue, wherein a message containing MT-Priority could be originated with a Message Submission Agent that does not know about this extension, and when the message hits a Message Transfer Agent that does support this, the header field will be turned back into a valid PRIORITY value, on the unwarranted assumption that it was authorized.  Intermediate MTAs have no way to distinguish this situation from one where the field was tunneled legitimately.

The counter-argument is that the use case for this specification involves out-of-band trust relationships, and that such situations will be known and dealt with.  Only by experimenting with it will we see how (or if) it can extend to other use cases where such trust relationships aren't as clean.

PROTO writeup for draft-melnikov-smtp-priority-tunneling-02

The publication of draft-melnikov-smtp-priority-tunneling as an
Experimental RFC is requested by an individual contributor.

(1) What type of RFC is being requested (BCP, Proposed Standard,
Internet Standard, Informational, Experimental, or Historic)?  Why
is this the proper type of RFC?  Is this type of RFC indicated in the
title page header?

This document proposes a protocol extension to its companion document,
draft-melnikov-smtp-priority.  Experimental was chosen because the new
mechanism of tunneling the SMTP parameters through servers that don't
support them by using reserved message header fields (see more below)
is of uncertain quality, and needs field experience.  The idea is not
deemed to be of Proposed Standard quality yet, without such
experimentation and experience.  The title page header says
"Experimental".

(2) The IESG approval announcement includes a Document Announcement
Write-Up. Please provide such a Document Announcement Write-Up. Recent
examples can be found in the "Action" announcements for approved
documents. The approval announcement contains the following sections:

Technical Summary

  Relevant content can frequently be found in the abstract
  and/or introduction of the document. If not, this may be
  an indication that there are deficiencies in the abstract
  or introduction.

This defines a mechanism for tunneling of SMTP (Simple Mail Transfer
Protocol) Message Transfer Priority values through MTAs (Message
Transfer Agents) that don't support the MT-PRIORITY SMTP extension.

Working Group Summary

  Was the document considered in any WG, and if so, why was
  it not adopted as a work item there? Was there controversy
  about particular points that caused the WG to not adopt the
  document?

There are currently no appropriate email-related working groups.  The
ADs and AppsAWG chairs considered the document for the Apps Area WG,
but decided that it would be done best as an individual submission,
and did not need the attention of the working group.

Document Quality

  Are there existing implementations of the protocol? Have a
  significant number of vendors indicated their plan to
  implement the specification? Are there any reviewers that
  merit special mention as having done a thorough review,
  e.g., one that resulted in important changes or a
  conclusion that the document had no substantive issues? If
  there was a MIB Doctor, Media Type or other expert review,
  what was its course (briefly)? In the case of a Media Type
  review, on what date was the request posted?

There is at least one prototype implementation, and plans for at least
one other after publication.  This is largely being done for a
particular use case, and the proponents are aware of some of the
tradeoffs they've made.  The shepherd has some concern about the
broader applicability of this as a standard, given those trade-offs.
That said, some of them had to be made, and there is value in
implementing features from proprietary email systems in standardized
ways on the open Internet.  The shepherd supports that general effort.

Personnel

  Who is the Document Shepherd? Who is the Responsible Area
  Director?

Barry Leiba is the document shepherd; Pete Resnick is the Responsible AD.

(3) Briefly describe the review of this document that was performed by
the Document Shepherd.  If this version of the document is not ready
for publication, please explain why the document is being forwarded to
the IESG.

This document began life recently, as a split-off of the parameter
tunneling aspect of draft-melnikov-smtp-priority.  Splitting that into
this experimental document, rather than having it on Standards Track,
as alleviated my concerns, echoed by others.  There does seem to be
consensus that it's worth trying this out, and that it's not terribly
unsafe to do so.  This document shares the trust model issues of the
other document (see below).

(4) Does the document Shepherd have any concerns about the depth or
breadth of the reviews that have been performed?

The proposal in this document has had sufficient review from the email
community, on the ietf-smtp list and through individual reviews, as
part of the review of its companion document.  I have no concerns
about the level of review.

(5) Do portions of the document need review from a particular or from
broader perspective, e.g., security, operational complexity, AAA, DNS,
DHCP, XML, or internationalization? If so, describe the review that
took place.

I would like to see SecDir and OpsDir reviews during the last-call process.

(6) Describe any specific concerns or issues that the Document Shepherd
has with this document that the Responsible Area Director and/or the
IESG should be aware of? For example, perhaps he or she is uncomfortable
with certain parts of the document, or has concerns whether there really
is a need for it. In any event, if the interested community has
discussed those issues and has indicated that it still wishes to advance
the document, detail those concerns here.

The tunneling of the PRIORITY value through non-conforming MTAs by
turning it into a message header field (MT-Priority) and then back
again is a problematic technique, but is an important capability for
those who need and intend to implement the smtp-priority extension.
It creates a trust issue, wherein a message containing MT-Priority can
be originated with a Message Submission Agent that does not know about
this extension, and when the message hits a Message Transfer Agent
that does support this, the header field will be turned back into a
valid PRIORITY value, on the unwarranted assumption that it was
authorized.  Intermediate MTAs have no way to distinguish this
situation from one where the field was tunneled legitimately.

The counter-argument is that the use case for this specification
involves out-of-band trust relationships, and that such situations
will be known and dealt with.  I believe that limits the usability of
those features on the open Internet, with other use cases.

(7) Has each author confirmed that any and all appropriate IPR
disclosures required for full conformance with the provisions of BCP 78
and BCP 79 have already been filed. If not, explain why.

Yes.

(8) Has an IPR disclosure been filed that references this document?
If so, summarize any discussion and conclusion regarding the IPR
disclosures.

No, and there are no known IPR issues with this document.

(9) How solid is the consensus of the interested community behind this
document? Does it represent the strong concurrence of a few individuals,
with others being silent, or does the interested community as a whole
understand and agree with it?

The consensus for this is solid, but relatively small.  A number of
participants/reviewers have expressed interest in the concept, though
it's not clear how much implementation is planned.

(10) Has anyone threatened an appeal or otherwise indicated extreme
discontent? If so, please summarise 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.

(11) Identify any ID nits the Document Shepherd has found in this
document. (See http://www.ietf.org/tools/idnits/ and the Internet-Drafts
Checklist). Boilerplate checks are not enough; this check needs to be
thorough.

The document refers to iana.org URLs at the shepherd's request, to
make it clear which registries are being referenced.  These URLs will
be removed before RFC publication.

(12) Describe how the document meets any required formal review
criteria, such as the MIB Doctor, media type, and URI type reviews.

No formal reviews are needed.

(13) Have all references within this document been identified as
either normative or informative?

Yes.

(14) Are there normative references to documents that are not ready for
advancement or are otherwise in an unclear state? If such normative
references exist, what is the plan for their completion?

This document has a normative reference to
draft-melnikov-smtp-priority, which will progress at the same time as
this one.

(15) Are there downward normative references references (see RFC 3967)?
If so, list these downward references to support the Area Director in
the Last Call procedure.

No.

(16) Will publication of this document change the status of any existing
RFCs? Are those RFCs listed on the title page header, listed in the
abstract, and discussed in the introduction? If the RFCs are not listed
in the Abstract and Introduction, explain why, and point to the part of
the document where the relationship of this document to the other RFCs
is discussed. If this information is not in the document, explain why
the interested community considers it unnecessary.

No documents are modified by this one.

(17) 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 protocol extensions that the document makes
are associated with the appropriate reservations in IANA registries.
Confirm that any referenced IANA registries have been clearly
identified. Confirm that newly created IANA registries include a
detailed specification of the initial contents for the registry, that
allocations procedures for future registrations are defined, and a
reasonable name for the new registry has been suggested (see RFC 5226).

The document contains one IANA action, which is clearly specified and
correct.  No new registries are created.

(18) List any new IANA registries that require Expert Review for future
allocations. Provide any public guidance that the IESG would find
useful in selecting the IANA Experts for these new registries.

None.

(19) Describe reviews and automated checks performed by to validate
sections of the document written in a formal language, such as XML code,
BNF rules, MIB definitions, etc.

I have run the usual idnits and ABNF checks, and all is OK.

IANA has reviewed draft-melnikov-smtp-priority-tunneling-02 and has the following comments:

IANA has a question about the IANA Action requested in this document.

IANA understands that, upon approval of this document, there is a single action
requested of IANA.

In the Permanent Message Header Field Names registry located at:

http://www.iana.org/assignments/message-headers/perm-headers.html

a new field name is to be added as follows:

Header field name: MT-Priority
Protocol: mail
Status: standard
Reference: [ RFC-to-be ]

IANA Question -> Currently the Permanent Message Header Field Names registry is
maintained through expert review as defined in RFC 5226. Has the document been
reviewed by the Well-Known URL registry expert?

IANA understands that this in the only action required to be completed upon
approval of this document.

Note: The actions requested in this document will not be completed
until the document has been approved for publication as an RFC.
This message is only to confirm what actions will be performed.

The following Last Call announcement was sent out:

From: The IESG
To: IETF-Announce
Reply-To: ietf@ietf.org
Subject: Last Call:  (Tunneling of SMTP Message Transfer Priorities) to Experimental RFC


The IESG has received a request from an individual submitter to consider
the following document:
- 'Tunneling of SMTP Message Transfer Priorities'
  as Experimental RFC

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
ietf@ietf.org mailing lists by 2012-07-02. 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 memo defines a mechanism for tunneling of SMTP (Simple Mail
  Transfer Protocol) Message Transfer Priority values through MTAs
  (Message Transfer Agents) that don't support the MT-PRIORITY SMTP
  extension.




The file can be obtained via
http://datatracker.ietf.org/doc/draft-melnikov-smtp-priority-tunneling/

IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-melnikov-smtp-priority-tunneling/ballot/


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