I’m a Eudora freak myself, and had no trouble setting up Avast even though it admittedly makes Eudora’s setup options, especially the servers, look funny.
Eudora really only needs your login name, your POP server (in my case, simply my domain), and your SMTP server (smtp-dot-domain for me), and it in effect “fills in the blanks” itself from there. With that as a starting point, the changes that Avast made to the server names worked just fine for me.