Re: The job of an MSA

[email protected] wrote:

> First, RFC 2746 is quite clear: Port 25 MAY be used for SUBMIT if for whatever
> reason 587 cannot be used.

2476 -- otherwise OK.

> More generally, what port something is run on is largely irrelevant; the
> important issues are service and protocol semantics.

If the protocols are to be treated as fundamentally different -- and 2476
says that an MSA runs ESMTP with some restrictions (N.B. not extensions) --
then that raises the question of how a client which connects to a server
on port 25 is able to determine whether that server is an MSA or an MTA.

> Of course this doesn't mean someone won't attempt to use SUBMIT-specific
> extensions in regular SMTP.

At the moment, as I understand it, there are no such "extensions", there
are only "restrictions" [RFC 2476 section 3.1].

> But just because some clueless ISP engages in
> egregiously bad practice is no reason to break our protocol specifications. I
> am dubious about the value of such an extension in any case for all the reason
> I've previsouly given; I would vehemently oppose making it part of regular
> SMTP.

It may be the case that presence of one or more hypothetical submission-
specific extensions might serve to distinguish an MSA from an MTA. That
would mean that the presence of such an extension would indicate that the
server in question is an MSA (running ESMTP), not an MTA (running ESMTP).

Of course if a particular MSA doesn't support any of the hypothetical
MSA-specific extensions, there is still the issue of how a client is
supposed to be able to determine whether it has connected to an MTA or
an MSA.  What do you suggest?