The Unsubscribe and Opt-out URL tokens to be included in CiviMail mailings point to a location in the Joomla backend. When clicked from the email, it directs the user to the Joomla admin login screen. These need to be rebuilt in order to allow unsubscribes/opt-outs from the general public.
On a related note –
I'd like to recommend the unsubscribe email or link NOT be required in order to send a mailing. Not all mailings are managed through a static group like a newsletter that can be unsubscribed from (the model used). It's putting a little too much power in the hands of the user to enable them to remove themselves from a group. For example, a membership organization sends mailings to all members, defined by a smart group. That's not something you would want the end user to unsubscribe themselves from, because it has other implications beyond the mailing.