Do you leave a copy of emails on the server?
Can you backup your Eudora mail data and uninstall/re-install?
Does this happen for all profiles (I assume that more than one user can use Eudora).
Have you tried replicating this with another client - e.g. Outlook Express?
Can you replicate it with Eudora and gmail / hotmail?
At some point you presumably did not have this issue. Is it possible to trace what has changed in the interim to start this happening? Updated / new firewall, updates to Eudora, new versions of AV / Malware etc. etc.?
SD