Re: [OT] Re: Can someone please explain this WAS: new photos from my party!

[Colin Watson <cjwatson@debian.org>]

On Tue, Jan 29, 2002 at 03:20:17AM +0100, Viktor Rosenfeld wrote:
> Colin Watson wrote:
> 
> > > > "From: bounce-debian-user=veitw=wsbt.de@lists.debian.org"
> > > 
> > > Nothing.  Everybody sees his own subscription address in the From:
> > > header.  Don't know why the mail appears to be bounced.
> > 
> > It doesn't. That's just where list deliveries to you get bounced, so
> > that the list can automatically unsubscribe people who aren't actually
> > receiving mail.
> 
> Hmm, maybe I had to much to much dope, but I can't really extract a lot
> of sense of your mail.  But then again, I don't have a lot of knowledge
> about mail in general or list-software in particular, so could you
> explain that to me?

OK. The mailing list software sets the "envelope sender" to
bounce-debian-user-<subscription-address>@lists.debian.org. This isn't
the From: line; it's the address that the mail claims to be from in SMTP
transactions, and in particular it's the address where delivery error
messages should be sent. [1] If mail to someone starts going wrong (say,
their mailbox fills up), these error messages will get sent back to the
mailing list software, it looks at the bounce-... address to see what
subscription address produced the errors, and unsubscribes that person.

[1] Sometimes there are broken mail setups that cause error messages to
    be sent to the address in the From: line rather than the envelope
    sender, so one person with a full mailbox ends up causing error
    messages to be sent to everyone who posts to the list. This is
    completely broken, and you're entitled to complain to their
    postmaster if you see it happening.

> Usually on debian-user, the address in the From: header is the same as
> in the X-Envelope-Sender:, except when purposely mangled by the sending
> machine, as is yours.  Or am I mixing something up?

The issue is confused by the fact that the spam didn't have a From: line
at all. Mailers do a variety of things to compensate for this, and one
common thing to do is that they make up a From: line from the envelope
sender (the one constructed by the mailing list - it "backs up" the
envelope sender from the original message it received in
X-Envelope-Sender:). This is why you're seeing strange effects.

I hope that was more comprehensible.

Cheers,

-- 
Colin Watson                                  [cjwatson@flatline.org.uk]