For multiple accounts, I have one In box and one Out box and one mailbox tree on Eudora ver 4.3.2, paid mode.
But, you are right, it is possible to set up separate directories for different users and pass the path to Eudora at invocation. Then you could have totally independent accounts. A family machine with multiple users and accounts would be set up that way. Each family member would have a shortcut icon on the desktop.
This should work for Karsten too.