In reply to:

I think this is a spammer technique. Probably Rubrick, Max or musick would be able to say more.

The thing is, I am getting "returns" from dozens of different domains:

postmaster@ resenterprises.com
MAILER-DAEMON@ mx.gwi.net
MAILER-DAEMON@ geocities.com
postmaster@npi.net
MAILER-DAEMON@ eve.nldesign.com
MAILER-DAEMON@ mail.mc.net
MAILER-DAEMON@ mail.bpsinet.com
etc


I think I am just going to bag it and start a new account somewhere.