Re: [Emailcore] Delivered-To issues

[Alessandro Vesely <[e-mail]>]

On Sun 03/Jan/2021 01:37:48 +0100 John C Klensin wrote:
> --On Saturday, January 2, 2021 21:56 +0000 Jeremy Harris wrote:
> 
>>> Should we be defining both, making it clear that they are
>>> different, and then making whatever recommendations seem
>>> appropriate about which one (or both) should be provided?
>> 
>> I agree that Envelope-To: and Delivered-To: are different.
>> 
>> I'm not convinced that this document is the right place
>> for either.  I guess there's a benefit in writing down the
>> definitions somewhere; the cost is "only" cruft that
>> obscures the minimum requirements for implementing an MTA.
> 
> My understand was that we had gotten to "separate document", or
> at least "not in 5321bis" some day ago.  I hope that is the case
> and that the perceived agreement holds.


This discussion brought up another defect of RFC 5321, methinks.  It does not 
define a straight line between an MTA and an MDA.  Section 4.4 says:

    When the delivery SMTP server makes the "final delivery" of a
    message, it inserts a return-path line at the beginning of the mail
    data.

Although the reasons for doing so are well explained, and are part of SMTP 
because of the reliability implications, inserting Return-Path: really looks 
like an MDA's job, not MTA's.  Perhaps, the text should say something like:

     When an SMTP server accepts a message for local delivery, it invokes a
     delivery agent passing to it the content and relevant parts of the
     envelope.  In particular, it MUST pass the <reverse-path>, which is used by
     the delivery agent to insert a return-path line at the beginning of the
     mail data.

In that case, mentioning that an MTA also passes the relevant <forward-path>, 
would not require to fulfill the steps (i)-(iv) of a previous message[*], 
because neither the MTA/MDA interface nor (all) the duties of MDAs are part of 
the specification.  Yet, it allows the I-D to mention non-normatively the names 
of Delivered-To:, Envelope-To:, and X-Original-To:.


jm2c
Ale
-- 

[*] https://mailarchive.ietf.org/arch/msg/emailcore/Vt1AboaP8j8rxnccedGvaLoPLyU