I don't have OE set to check messages, I always run mailwasher first, then manually download messages. My AV is the same one I have used for almost 8 years and was updated several months ago.
The only program that sends out periodic e-mails automatically is Visualzone to the GShield web site, have tried it with that disabled and it still does it. It does not seem to be causing any other problems but you know how annoying things like this can be.