MTAs that pass SMTP AUTH?

[Scott Balmos]

Okay, maybe this might be a better question... In the O'Reilly "Managing IMAP" 
example (http://www.oreilly.com/catalog/mimap/chapter/ch09.html#91630), it 
discusses the setup I need, where some folders have per-user +p access. In 
the example case, msmith and johndoe.

It says that msmith & johndoe, sending to the submission address of 
announce+events at yourdomain.com, can go through fine, while others' 
submissions get dumped to announce's inbox. This is all supposedly "standard" 
through the deliver(8) program, and that a Sendmail config script handles it 
all.

My question is, where is Sendmail getting, or even sending to the deliver 
program, the information that says to match against username msmith, johndoe, 
or whatnot? I know of the -a switch for deliver, but pretty much all the 
other MTAs (including Postfix) say that there can only exist a "blanket" 
Cyrus user, designated to the MTA, for posting to shared folders.

Where's everything come from, authentication-wise? The only thing I can think 
of is the user creates a message, saves to their local drafts folder, then 
manually "moves" the message into the proper folder on IMAP. But that seems 
really icky, and essentially like "IMAP Send".

Am I missing something? Thanks.

--
Scott Balmos