[pkg-fetchmail-maint] Bug#349726: fetchmail: MAIL FROM: derived from Return-Path may cause double-bounces and bounceloops

[Matthias Andree]

Andreas Beck <becka-debbug at bedatec.de> writes:

> However, when downloading via POP, the return path of bounces is usually
> set to the mailer daemon that sent the bounce,

...which would constitute a bug. It's not entirely clear what exactly
you mean, I'll try my best to answer:

> as the mailserver that delivers to the POP-box sets it, as it does
> (from its point of view) a final delivery.

Bounces are to be sent with NULL envelope sender, fetchmail fails at
that (Bug#316446, fixed in 6.3.0) and the vast majority of bounces I am
downloading with fetchmail have "Return-Path: <>" as their first line...

Bounces (rather than SMTP rejects) are a more general problem, see also
Bug#146306 (still open).

fetchmail 6.3.0 and newer versions use a null envelope sender (reverse
path) for the fetchmail-generated bounces, thanks to Holger Mauermann's
bounce patch (the patch fixed other annoyances in bounces, too). This
null reverse path is hardwired in the bounce code.

Generating bounce loops however requires feeding the bounce back to
fetchmail's POP3 box somehow, which usually means the fetchmail-daemon@
alias is missing on the local system or forwarding to a domain that
fetchmail is supposed to fetch.

> The feature I request would that be to introduce an option
> "envelopefrom" or similar, that works on the MAIL FROM: line just like 
> the "envelope" option does for the RCPT TO:.
>
> The option should default to "Return-path", thus keeping backward
> compatibility.

I have yet to see a site that would use a custom header instead of
Return-Path, and I don't see how that custom header would be any more
reliable or useful than Return-Path. The latter is supposed to contain
the reverse path. I don't think adding another option is of use here.

Backporting the compatible parts of Holger Mauermann's bounce patch for
Debian's sarge release might be worth considering though. The diff is
archived at Rob Funk's site and I believe also in the list.ccil.org
archives for the fetchmail-friends list.

NOTE: The patch isn't suitable for direct application to sarge and needs
to be stripped of incompatible changes (such as changing the From:
header or the bounce message text):
<http://funknet.net/fetchmail/patches/2003-10-23-6.2.5-mauermann-bounce.diff>

-- 
Matthias Andree