Hello,
Sounds like a couple of people are a bit frustrated, so I'll clarify how we've set it up.
We all know that spamassasin doesn't come enabled on systems, which means the spamd program will not be running. The interface checks to see if it's running before letting the clients into the control panel. If you want it off, then don't run the spamd (and don't enable it in your exim.conf).
Spamassassin is setup per client account, since it's stored in /home/username/.spamassassin/user_prefs. The interface is provided for all domains even though it's only saved in 1 location. There is a difference between domains only in that you can route spam with the first option.
I can look into a "condition" for turning it off. It would be a simple addition to the exim.conf where if the user_prefs file doesn't exist, spamassassin is not run for that user. To turn it off, just delete the user_prefs (ill provide a button for the user).
Spamassassin works fine on a per system-user basis for the time being. We can consider adding it for per-inbox at a later date, but for the time being we'll stick with per client account.
John