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What is the difference between MAIL CONTROL and Forefront's POLICY RULES?
It seems they serve a similar purpose.
Mail Control always sets operations on mails that sent into Outlook Web App. It includes Rules, Domains &Protection, Journaling and Delivery Reports.
Policy Rules in Forefront Online Protection for Exchange is to set rules not only for inbound messages, but also for outbound messages. Moreover, the rules are set generally because of safety concerns.