Remember, Outlook is covered by the Outlook/Exchange provider, so as far as you see the avast Outlook/Exchange splash screen when starting Outlook, you should be OK.

Now I remember – it’s possible that the plugin actually didn’t get registered because at the time you were installing avast, Outlook was not on your machine. In that case, it might help (besides reinstalling avast) to go to the Control Panel, Add/Remove programs, and first remove the Outlook/Exchange avast provider and then reinstall it back…

Thanks
Vlk