From:, Mail, and sendmail

[eric%ucbarpa at UCB-VAX.ARPA]

From:  Eric Allman <eric%ucbarpa at UCB-VAX.ARPA>

The problem with using the UNIX-style "From" line as a return address
is that it is not necessarily the sender of the message.  It corresponds
to the "Return-Path:" field in Arpa-land, which is really the address
to send delivery errors to.

In UNIX these have traditionally been the same (he who sends the mail
gets the errors), but that is changing.  Several sites now change that
address when they forward messages to a list.  For example, mail to
"INFO-UNIX at BRL-VGR.ARPA" is resent "From INFO-UNIX-REQUEST at BRL-VGR.ARPA".

My belief is that the "correct" solution is to eliminate routing from
the addresses, so that it would not be necessary to rewrite headers
on the fly.  For example, a reasonable address would be "eric at ucbvax.UUCP"
no matter where you were sitting on the net.  [Peter Honeyman would
accuse me of being an at-ist (he proudly admits to being a bang-ist),
but you can't have everything.]  The "uucp project" is putting together
software now that appears to have this functionality.

eric