I have a few e-mail aliases that forward to external hosts. Currently, if the external host rejects a message, Exim generates a bounce message and sends it to the original sender. This is bad because if the external host rejects the message as spam (a common case), then I'm a source of backscatter spam.
Thus, if the sender is non-local, I'd like to send the bounce to postmaster (me) instead. Alternately, sending all bounces to postmaster would be good enough.
The Exim documentation hints that this can be done ("when a message fails to be delivered ... Exim sends a message to the original sender, or to an alternative configured address", emphasis added), but I couldn't find how.
For example, here is a log excerpt showing a backscatter spam being created (in this case, the purported source server isn't accepting connections).
email@example.com is the purported sender of a spam e-mail to
firstname.lastname@example.org, which then forwards to
email@example.com; GMail then rejects the message and my server creates a bounce to
firstname.lastname@example.org. I want that bounce to go to
email@example.com instead. (Usernames obfuscated; the rest of the log is verbatim.)
2011-10-03 12:03:08 1RAkyw-0000cj-45 <= firstname.lastname@example.org H=(gyajnj.com [18.104.22.168] P=esmtp S=33927 email@example.com 2011-10-03 12:03:09 1RAkyw-0000cj-45 ** firstname.lastname@example.org <email@example.com> R=dnslookup T=remote_smtp: SMTP error from remote mail server after end of data: host gmail-smtp-in.l.google.com [22.214.171.124]: 552-5.7.0 Our system detected an illegal attachment on your message. Please\n552-5.7.0 visit http://mail.google.com/support/bin/answer.py?answer=6590 to\n552 5.7.0 review our attachment guidelines. i3si13239001yhk.107 2011-10-03 12:03:09 1RAkyz-0000cm-H5 <= <> R=1RAkyw-0000cj-45 U=Debian-exim P=local S=35124 2011-10-03 12:03:09 1RAkyw-0000cj-45 Completed 2011-10-03 12:03:30 1RAkyz-0000cm-H5 nacha.net [126.96.36.199] Connection timed out 2011-10-03 12:03:30 1RAkyz-0000cm-H5 == firstname.lastname@example.org R=dnslookup T=remote_smtp defer (110): Connection timed out
Here is the relevant router:
dnslookup: debug_print = "R: dnslookup for $local_part@$domain" driver = dnslookup domains = ! +local_domains transport = remote_smtp same_domain_copy_routing = yes # ignore private rfc1918 and APIPA addresses ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8 : 192.168.0.0/16 :\ 172.16.0.0/12 : 10.0.0.0/8 : 169.254.0.0/16 :\ 255.255.255.255 no_more