well I just got an email about subscription ( well they put it as email list) anyway if you subscribed to a forum then you just started receiving emails about post in from the forum you subscribed to a while ago.
I was working on some cron scripts & subscription are working now. so if you don't want it then go to My Home link then find the edit button Subscribe / Unsubscribe from receiving forum posts by email, change message notifications, etc.

(S - Subscribe ; U - Unsubscribe)

Thanks