Felipe, welcome to avast forums.

I think the best you can do is download the version 4.5 Beta because, like you said, it uses a new mail detection that will work automatically. Please, set up your email account just as avast does not exists and then update avast to 4.5 version. It will detect the pop3/smpt/imap ports and scan your messages.

Instructions here: http://forum.avast.com/index.php?board=11;action=display;threadid=8044;start=0

Can you make a try and see if it’s ok? Thanks.