Perhaps you should consider installing & using a program
that "specializes" in detecting & removing worms, trojans,
generic dialers, etc called "Ewido" from www.ewido.net/en.
This assumes your OS is either Win 2000 or Win XP; there
is a "tutorial" on this program at www.greyknight17.com/spy/Tutorials/ewidoQuickGuide.pdf .
Well if it is coming in by email avast can only detect it and give the option to delete it, it can’t stop it being sent and sent and sent. You could add the from email address to your blocked senders list but I doubt that would be helpful as 1) it is scanned before it gets to your email program and the email address is likely faked and likely to change.
There are anti-spam tools that check a small piece of each email and can delete it at server level, so it doesn’t get to you to be scanned. I use MailWasher Pro, although it is primarily for Spam it is also easy to deal with suspicious emails, you can check for suspicious or infected emails and mark them for deletion. There is a free version, but this only works with a single email account. The Pro version works with multiple accounts.
You can search but you shouldn’t find anything because the avast email scanner deletes it before it gets to your in-box so it shouldn’t be on your HDD. So there shouldn’t be anything else to do.