sa-learn all users
 

I am at them moment running a crontab on every individual user
sa-learn --spam --mbox /home/spam/mail/inbox

but i want to setup a global .spamassasin where all users are accessing this file so i do not have to do an sa-learn for all users.

Thanks

You would probably be able to do that by having your MTA route all incoming mail through spamassassin before it is distributed.

If you don't have them already, you can download rulesets from the spamassassin website to increase the accuracy of spamassassin. They filter based on header, subject, sender, body content, etc.