Robert_Charlton - 3:06 am on Feb 8, 2010 (gmt 0)

Perhaps you have something like "username@example.com"<junk>

You don't have to have <junk> in the address area to have a problem with this. In my experience, the "@" character in the display name area is enough to get an email immediately kicked back, as in...

UserName@example.com <username@example.com>