If you only have one mail account in your Eudora, click on the
Tools menu and select Options...
In the options screen, click on the Sending Mail icon and select
the check box labeled Allow authentication. Click Ok and you are
If you are running multiple accounts, click on the Tools menu, then
the Personalities option. In the Personalities window, select
your MainTree account and select Properties.
In the Generic Properties, select the Authentication Allowed check
box then click Ok and you are done.