I realize that this should be an Avast problem, but I cannot get an answer
anywhere else. If anyone is familiar with this problem, I would be
greatful
for a solution.

I.ve been using Avast free version for years with OE with no sending or
receiving issues.

I'd suggest right clicking the Avast icon (in the tray) - then 'Program
settings' - then the 'Help' button - then select the Outlook Express
settings (you get one for sending and a 2nd for receiving)

Your solutions will undoubtedly follow.

Blithe