I too would suggest you only check the first option.

The second doesn’t actually scan anything, just that Outlook won’t let you save or send attachments that ‘might’ be a virus and they do this on nothing more than the file type of the attachment. You wouldn’t believe some of the pathetic file types it considers dangerous, I believe .zip files are included in this ‘dangerous’ list. Considering a zip file must first be unpacked and second execute the file/s inside and before you could do that avast would scan it.

So I would say your common sense should be a damn sight better than this pathetic measure, don’t open attachments or click links in unsolicited emails. Even if the email isn’t unsolicited, never open the attachment directly from the email, save it to your HDD where avast ‘should’ scan it. I would also suggest you do a right click (ashQuick) context menu scan of the file.