Hallo,
I've installed version 1.4 of moodle and am working through it. Subscribing to email-information is possible at several points. But I could not find points to disable automatic emails.[1] A good place would be, in my opinion, the profile, where the selection could offer no "no mail at all".
Thanks
Herbert Plass
Vienna/Austria
[1] Thats not really true: This mask (discussion entry) contains a dropdown menue to unsubscribe emails. But do I have to post something in order to change my preferences?
Just go to the forums list and there is a column to toggle subsription for each forum
I've got it! 
Also note the little eye next to the email address in your profile ... it will disable/enable ALL your Moodle email completely regardless of subscriptions. Useful when going on holidays, for example.