[pkg-fetchmail-maint] Bug#316446: Invents invalid from address for bounce messages received with null reverse path

[Roger Lynn]

In addition to sending bounce messages with a non-null reverse path, I 
have also discovered that Fetchmail invents a from address for bounce 
messages received with a null reverse path, consisting of 
<username>@<POP3 servername>, which in my case is not a valid address.

If a spam is forged as coming from a non-existent address on my machine, 
and bounces, Fetchmail will receive the bounce, find it can't deliver it 
and send a new bounce message to the from address it has just invented. 
This in turn will also bounce. The only reason I haven't had mail loops 
is because I added a mail alias for FETCHMAIL-DAEMON, so that bounces 
which bounce back to that address don't themselves generate new bounces.

An example is shown below. Using the SDPS protocol, the *ENV command is 
used to obtain the envelope to and from addresses. This is documented at 
http://www.demon.net/helpdesk/producthelp/mail/sdps-tech.html/
I haven't been able to force Fetchmail to use standard POP3 as the 
protocol option appears to be ignored.

fetchmail: starting fetchmail 6.2.5 daemon 
fetchmail: 6.2.5 querying pop3.demon.co.uk (protocol POP3) at Fri 22 Jul 2005 17:30:13 BST: poll started
fetchmail: POP3< +OK demon POP3 server ready (demon.co.uk)
fetchmail: POP3> USER rilynn
fetchmail: POP3< +OK 
fetchmail: POP3> PASS *
fetchmail: POP3< +OK 
fetchmail: selecting or re-polling default folder
fetchmail: POP3> STAT
fetchmail: POP3< +OK 1 2153
fetchmail: 1 message for rilynn at pop3.demon.co.uk (2153 octets).
fetchmail: POP3> LIST 1
fetchmail: POP3< +OK 1 2153
fetchmail: POP3> *ENV 1
fetchmail: POP3< +OK 
fetchmail: POP3< ok
fetchmail: POP3< rilynn.demon.co.uk
fetchmail: POP3< 

*** The line above is the envelope from address.
    Below is the envelope to address.            ***

fetchmail: POP3< roger at rilynn.demon.co.uk
fetchmail: POP3< .
fetchmail: POP3> RETR 1
fetchmail: POP3< +OK 
fetchmail: reading message rilynn at pop3.demon.co.uk:1 of 1 (2153 octets)
fetchmail: passed through roger at rilynn.demon.co.uk matching rilynn.demon.co.uk
fetchmail: SMTP< 220 rilynn.demon.co.uk ESMTP Exim 4.50 Fri, 22 Jul 2005 17:30:17 +0100
fetchmail: SMTP> EHLO localhost
fetchmail: SMTP< 250-rilynn.demon.co.uk Hello localhost [127.0.0.1]
fetchmail: SMTP< 250-SIZE 52428800
fetchmail: SMTP< 250-PIPELINING
fetchmail: SMTP< 250 HELP
fetchmail: forwarding to localhost
fetchmail: SMTP> MAIL FROM:<rilynn at pop3.demon.co.uk> SIZE=2153

*** Above Fetchmail has invented an invalid envelope from address,
    which is where any Delivery Status Notifications will be sent. ***

fetchmail: SMTP< 250 OK
fetchmail: SMTP> RCPT TO:<roger at rilynn.demon.co.uk>
fetchmail: SMTP< 250 Accepted


The Return-path: header, obtained by telnetting to the POP3 server is:

Return-path: <>

By the time it has arrived in my mailbox this has become:

Return-path: rilynn at pop3.demon.co.uk


Regards,

Roger