I think this one is cute. Do you reject AOL bounces or is someone doing
a dictionary attack spoofing your domain with random usernames and the
AOL system is unable to deliver the bounced email to your system. You'd
think they'd filter out the "User unknown"'s.
I just received 2 copies of this email from AOL's Postmaster, and it looks
genuine. We filter via SpamAssassin, but do not bounce spam or virii, but
divert them to separate folders.
2) Total percentage of bounces accepted by pil.net (lower than 90% acceptance): 74%