Philip Hazel wrote:
Summary of the Bcc discussion: posted to exim-users, exim-dev, & ietf-822
There were a few responses on the exim-users mailing list. There was a
longer discussion on the ietf-822 mailing list,
[...]
2. Other discussion
Some interesting points of clarification came up in the discussion. The
functions of mail handling are now seen as split into four distinct
parts, as follows:
MUA -> MSA -> MTA -> MDA -> MUA
(user agent, submission agent, transfer agent, delivery agent).
Question: Is there an RFC where these terms as used here are defined?
I couldn't find one (in particular, the only reference to "MDA" that
I was able to find was in RFC 3528, which has nothing to do with this
topic).
Aside: I am aware of diagrams in RFCs 2821 and 3464, but they only
show part of the chain; 2821 deals only with SMTP client/server with
no distinction among MSA/MTA/MDA, and 3464 deals only with "MTA"s. I
am also aware of Patrik Faltstrom's "mailflows" diagram, but again
that simply refers to everything as "MTA".
Additions: Typically there is a message store of some sort into which
the MDA places messages. There may also be a message access server
(MAS) between that message store and the recipient MUA. The MAS is
typically a POP variant or IMAP server. And of course gateways to/
from non-SMTP/POP/IMAP mail exist.