My wife lost the service for a daily email. I've checked with the sender and she is still on his distribution list. She uses Gmail and MS Mail in Vista, SP2. No filter for the sender's site on Gmail server or MS Mail on her hard drive. She uses Norton 360, but no blockage there. Her last message was on May 23rd.
I've asked the sender to remove her from his list and have her start a new account, but haven't heard from him yet.