You can make a search (see the button above) into the forums with “The Bat”. The answer to your question is “YES”: avast! supports MS Outlook (including Outlook 2003), MS Exchange, MS Outlook Express, Eudora, Pegasus Mail, Netscape Mail, Mozilla Mail, IncrediMail and The Bat! as Internet Mail Clients.
Wellcome to avast! and to the forums!