[news.sysadmin] "From:" vs. "From_"

vixie@decwrl.dec.com (Paul A Vixie) (12/04/88)

Since it is essentially on my advice that pacbell does what it does, I'd better
answer this before David gets worried...  Note the Followup-To: and please
respect it.

[Kantor]
# Nearly every one of the bounced messages turns out to be a reply to mail
# that passed through host 'pacbell' before it got to ames.  'pacbell'
# doesn't add its sitename to the "From:" line in mail, but does add it to
# the "From " line.
# [...]
# The system administrator at host 'pacbell' claims he's doing the right
# thing.  I think he's wrong.  There it stands.

And I think he's right.  Is that as far as we're going to get?

Some sites add their names to From: lines, some don't.

All (uucp) sites add their names to From_ lines.

Mailers that depend on being able to send back to a From: line will run into
many RFC976-compliant mailers out there that leave it in "user@dom.ain"
format -- so they'd better run routers of some kind -- and many other mailers
that break a perfectly good "user@dom.ain" by prepending their hostname and
a bang to it, thereby creating a mixed address.  Third order effects of this
are far and wide -- like mailers that try to "fix" mixed addresses for you,
etc.

My assertions on this topic:

(1) smart mail user agents or mail user agents that can depend on a smart
  transport (that is: elm or any user agent that knows it's talking to smail)
  should reply to "From:" addresses, since they _are_ supposed to be addresses.

(2) dumb user agents or any user agent that knows it's talking to a dumb
  transport should use the From_ retuyrn-path (since it _is_ a path).

(3) mailer user agents that cannot be made to do the right thing should be
  fixed.

(4) the non-gateway transports that modify "From:" addresses should be rm'd.

(5) given that some transports modify "From:" and some do not, the direction
  we need to move toward is getting them all (except gateways) to _not_
  modify "From:".

--
Paul Vixie
Work:    vixie@decwrl.dec.com    decwrl!vixie    +1 415 853 6600
Play:    paul@vixie.sf.ca.us     vixie!paul      +1 415 864 7013