The provider you must configurate is the Internet Mail.
Choose if you want to scan the Inbound and/or Outbound Mail and if you want to add a note at the end of each email to know it was scanned.

If you try to read the avast! help file for this provider you will be able to configure it with easy. If you cannot do it, please ask specific questions and we will answer you.

Generally, when avast! found a virus you will see a popup Window of alert and can choose the action to do. :wink: