On Tue, 13 Jul 2004, Markus Hofmann wrote:
what we need to solve now is the issue with respect to "what SMTP
element to focus on first", and whether distinguishing between SMTP
elements makes sense - see below from earlier emails.
...
So, following questions:
(a) Does it make sense to distinguish between different SMTP roles?
For those like me, fuzzy on MUA, MSA, MTA, and MDA definitions, here
is some text I found (please post better references if available!)
RFC 2821 says:
SMTP servers and clients provide a mail transport service
and therefore act as "Mail Transfer Agents" (MTAs). "Mail User
Agents" (MUAs or UAs) are normally thought of as the sources and
targets of mail. At the source, an MUA might collect mail to be
transmitted from a user and hand it off to an MTA; the final
("delivery") MTA would be thought of as handing the mail off to an
MUA (or at least transferring responsibility to it, e.g., by
depositing the message in a "message store"). However, while these
terms are used with at least the appearance of great precision in
other environments, the implied boundaries between MUAs and MTAs
often do not accurately match common, and conforming, practices with
Internet mail. Hence, the reader should be cautious about inferring
the strong relationships and responsibilities that might be implied
if these terms were used elsewhere.
http://www.ietf.org/internet-drafts/draft-hutzler-spamops-00.txt says:
The Internet email architecture distinguishes four message-handling
components:
o Mail User Agents (MUAs)
o Mail Submission Agents (MSAs)
o Mail Transfer Agents (MTAs)
o Mail Delivery Agents (MDAs)
At the origination end, an MUA works on behalf of end-users to create
a message and performs initial "submission" into the transmission
infrastructure, via an MSA. An MSA accepts the message submission,
performs any necessary pre- processing on the message and relays the
message to an MTA for transmission. MTAs relay messages to other
MTAs, in a sequence reaching a destination MDA that, in turn,
delivers the email to the recipient's inbox. The inbox is part of the
recipient-side MUA that works on behalf of the end-user to process
received mail.
These architectural components are often compressed, such as having
the same software do MSA, MTA and MDA functions. However the
requirements for each of these components of the architecture are
becoming more extensive, so that their separation is increasingly
common.
Given the above, I think MTA is an appropriate first target. Since we
are OPES, we should be looking for an intermediary here. Targeting
MUAs would be like targeting browsers in OCP/HTTP profile, right? The
latter is not theoretically inappropriate (nobody can clearly define
what an intermediary or "edge" is), but also not important enough for
OPES right now.
Moreover, could we try to simplify the charter by removing all other
SMTP agents from it? Can we just hope that OCP/SMTP profile with a
focus on MTAs will be applicable enough to MSAs and MDAs? We can
always add MSA- or MDA-specific features later, right?
Thanks,
Alex.