Under General menu there is Register menu item.
Just create any test user and then login into Mail app.
It doesn't support mail delivery, in order to see message in mail folder you can create folder, in preferrences assign this folder as Sent folder and then send email somewhere. Copy of the message will be saved in Sent folder.
Sorry if it is too much trouble make it work, but as i understood there were some concernes hot ns_mail IMAP modules may be used in AOLserver.