Double click on the avast 'a' icon, if you see a details button at the bottom of the window, click it, select the Outlook/Exchange icon and select it, click Start, answer Yes to persist change.
If you are only using MS Outlook you don't really need the Internet Mail provider running, however, it provides a useful indication if you have a spambot sending email from your system (but the sensitivity would need to be High). You regular mail using MS Outlook would be scanned via the outlook plug-in.