backscatter.

 If you’re receiving messages saying an email has bounced, or is “undeliverable”, and you’re sure that the email could not have come from you (or malware on your computer/server), then you’re receiving backscatter. If you’re using Exim, you can make the following change to cut down the amount of backscatter you receive:

1. Go to WHM »Service Configuration »Exim Configuration Manager
2. Click on “Advanced Editor”
3. Look for “custom_begin_rbl”.
4. Paste the following code in that box:
   Code: deny senders = : MAILER-DAEMON@* postmaster@* dnslists = ips.backscatterer.org log_message = $sender_host_address listed at $dnslist_domain message = Backscatter: $dnslist_text
5. Save. I think this restarts Exim… if not, do it yourself.

What this does is check the backscatterer.org blacklist, and blocks only the automated bounced messages that come from those domains.