You have an Exchange Server 2010 organization. You deploy an Edge Transport server.  You need to implement a message hygiene solution that meets the following requirements： .Users must be able to receive e-mail from external recipients who have been added to their Safe SendersLists .The Edge Transport server must block all e-mail sent to invalid addresses inside the organization  What should you do first？（）

• A、Enable sender filtering.
• B、Create Send connectors.
• C、Configure real-time block lists （RBLs）.
• D、Configure EdgeSync synchronization.