Technical, he is using Outlook Express, not MS Outlook (correct me if I'm wrong). He needs to start INTERNET MAIL provider in Avast! On Access Scanner, not the Outlook/Exchange.
BalaR - MS Outlook and Outlook Express are completely two different e-mail clients. If you don't use Outlook, then go to On-Access scanner and terminate OUTLOOK/EXCHANGE provider... you don't need that.
For protecting your accounts in Outlook Express, you need to have Internet Mail provider started.
Cheers !