ODMR is better than POP in retaining the message envelope and not having
the "keep mail on server" loophole.
Loophole?
C: mail from:<alice@a>
S: 250 ok
C: rcpt to:<bob@b>
S: 250 ok
C: data
S: 354 send it
C: blah blah
C: .
S: 452 keep mail on server
For mail reinjected after delivery, there has long been a convention
to retrieve the envelope from the Return-Path: and Delivered-To: or
X-Envelope-To: headers at the top of the message. Fetchmail does it,
qmail's serialmail does it.
That's one of those things that probably would have been worth puting
in a standards track RFC long ago, but it's too late now.
R's,
John