The line below is an example of text in the response to undeliverd mail that explains the cause of the bounce.  In this case it is a spam filter called SpamCop which our host employs to minimize spam on our lists.  SpamCop is and example of a Realtime Block List (RBL).  An RBL is a list of IP addresses maintained by an independent party that identifies mail servers on the Internet that are known to have sent spam mail.

         <<< 553 Blocked - see http://www.spamcop.net/bl.shtml?205.188.157.35

“How is that possible?” you ask, “I have sent no spam from my email account.”

Regrettably identifying the source of spam is a very difficult and sometimes impossible task.  In the effort to address the outcry from email users about spam several less than perfect techniques have been adopted by the spam filters so that they do ‘the best they can’ despite some false positive results.

In this case SpamCop has at some point received some spam messages from the server in question, either sent by a bogus user of that mail server, or sent by another server but made to look as though it is coming from the this server (a process called 'spoofing').  SpamCop walks the email header information to determine the unique address of the sending server (205.188.157.35) and adds that to its ‘bad’ list.  When one of our email lists gets a message our host server performs the same analysis to determine the sending server’s address.  It then asks SpamCop and some other RBL’s if this is a known bad address.  If the answer is ‘yes’, it automatically responds to the message with a failure and does not complete delivery.

The good news is that a huge email provider like AOL utilizes many outgoing email servers.  When you send a message it may be sent from any number of server addresses.  That is why some of your email is getting through, it has been fortuitously sent via a server that has not been identified as a spam source.  In fact if you look at the details for this listing you will see this address has been listed for only 27 hours out of the past 359 days.

What’s the solution?  The ideal solution is to let the mail server owner know their server is on the SpamCop list and have them work with SpamCop to get it removed.  Even if they don't SpamCop will automatically delist the address after a certain period of time if they receive no more spam attributable to it.  Unfortunately the spammers may employ this server’s address again and perpetuate the problem.

There’s the RBL snafu in a nutshell.  Both parties involved (the email server owner and SpamCop) are independent of our host.  Our host merely subscribes to a free service widely accepted to be among the best.  The alternative to using such filters is that a large number of spam email is delivered to our list subscribers every day which they must filter themselves - the greater of two regrettable evils.