From Simeon Leifer:
If you use Eudora, use OS X, and would actually like to know when you have new email, you want MailLight. MailLight adds an icon to the menubar to tell you when you have unread mail waiting in Eudora. Use the drop down menu to bring Eudora to the foreground.
You can control how often MailLight checks to see if you have new mail.
You can set MailLight to ignore any mailboxes you choose.
MailLight does not show up in your Dock unless you want it to.