The important number for Blocker is the number of actual users who are sending/receiving mail through Blocker. Mailboxes are not counted, rather # of users. Customers should plan their initial purchase for the number of users they expect to have for the duration of the subscription. If they exceed the number of users during the subscription period, Blocker will still process the extra users' mail. It's primarily an honor system although there are considerations to put in place to alert and take action against serious abusers who try to exceed 250 users. So make the initial purchase decision based on most accurate data for number of users to be covered, and when its time to renew, if you are over, buy the higher user subscription.
