From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 21 Oct 1993 23:12:11 -0400 From: David Hogan dhog@cs.su.oz.au Subject: wayward mail Topicbox-Message-UUID: fdcf4518-eac7-11e9-9e20-41e7f4b1d025 Message-ID: <19931022031211.1Tbtz1mR7oayUOJY6mbeRDCcPM1Mosop8oXoFYXETtg@z> > From: Scott Schwartz > > | not quite... upas uses the SMTP information, not the message contents, > | as i think it should. > > Well, ok, but the local postmasters tell me that the internet > conventions are otherwise. Indeed they are. On the internet, all mail messages are supposed to be formatted according to rfc-822, with the headers indicating who the actual sender and recipient(s) are. The SMTP information (aka envelope) is part of the delivery mechanism, usually derived from those headers, but not necessarily equivalent to them. In particular, when a mailing list expander receives some mail, say to 9fans@cse.psu.edu, it sends out an essentially identical piece of mail (same rfc-822 From and To headers) but with a different SMTP envelope: the envelope sender becomes an alias for the maintainer of the list (9fans-request@cse.psu.edu), and the recipients are the members of the list. This is good, because bounces go back to the list maintainer (who is most likely to be able to do something about them) but replies go to the list and/or the original sender, depending on the behaviour of the user agent (and the user driving it). The difference between the rfc-822 headers and the envelope is also used to ensure that a bounce doesn't generate another bounce, which could lead to loops, by having the mail software use a null envelope sender when it sends the bounce message. I understand that at Bell Labs the mail conventions are quite different (and in fact much simpler). The contents of a mail message are unformatted (ie no rfc-822 or anything) and are deposited in your mailbox with a single From line prepended, which will be the SMTP envelope sender if the mail arrived via SMTP. The mail user agent (upas/edmail) replies to the address in the From line (it doesn't have much choice :-). Unfortunately, these two sets of mail conventions aren't always compatible, and in particular they break down when internet mailing lists are involved. I have to say that I prefer rfc-822, since (amongst other things) it lets you know who the _other_ recipients of the message were (assuming the sender wanted you to know this :-)