Did you try the time honored method of disabling your antivirus product. They are more than capable of showing just how poorly they are written by blocking all mail if even the slightest thing in one of your emails is not how it wants things to be.

Some folk get short term relief by deleting everything in the web mail spam folder, as they are the most likely to cause an antivirus program to step on itself. But essentially products that scan incoming POP3 emails are becoming ever less reliable. It might be a factor of cheaper retail prices, but I have gone with no email scanning using windows defender.

Thanks Matt. I use Norton and have turned off email virus scanning. I have deleted items in the Webmail junk folder. My ISP's spam filter keeps putting valid emails (some from the same sender get through and some don't) in Junk so I don't see than. I move them to the Inbox and they eventually download. No solution yet.