Andy62,
I wonder why you would be going to this trouble when, if the avast Internet Mail scanner is active on your system your regular POP3 email accounts will have already been automatically scanned by avast before they reach your OE Inbox.
Do you have accounts that cannot be scanned by the Internet Mail scanner?
If you are planning to do manual scans then, as mentioned by DavidR, ashquick.exe will provide a more thorough scan of your email attachments including the contents of archive type files (like .zip).