I've been using Foxmail at least since it's 3.0 version. Of all the anti-virus programs, Jiangmin (from China) works the best for Foxmail. However, I dumped it soon after I tried Avast, and never had any problems ever since.
Never used Foxmail to download Hotmail or Yahoo mail, 'cause it's way too slow(with or without any protection). For normal pop accounts, never had any problem with Avast. Here's my settings:
POP3 & SMTP all set to 127.0.0.1
username set to username#domain (if your email address is abc@email.com, then the username here should be abc#email.com)
password: just your password
Then you're Ok, shouldn't be any problems.
Now using Avast to scan and delete your old mails is a bit tricky, if you do have infected old mails:
1.Export all the mails from one of your mail boxes to a directory.
2.Let Avast scan that directory
3.Open the infected files Avast found, check the date & time of the email
4.Go back to Foxmail, locate the infected mail in your mail box, delete it.
5.Not done yet! You just deleted it from the index file, the virus data is still in the box file. From "box" menu, click "compress", the virus data is deleted
6.Not done yet! When you delete the mail, the mail is moved to your trashbox file. So you must click the trash box, click "empty trashbox" in "box" menu, then "compress". Done. This individual infected mail is completely removed from your Foxmail.