Your network contains two Exchange Server 2010 Edge Transport servers and five Exchange Server2010 Hub Transport servers.  All e-mail sent from your organization to the Internet is transferred by the Edge Transport servers. You need to recommend a security solution for the organization to meet the following requirements： .Ensure that users can send encrypted messages to any other organization on the Internet  .Ensure that all Exchange-related communication between Hub Transport servers and Edge Transport servers is encrypted What should you recommend？（）

• A、Deploy IPsec.
• B、Deploy SMTP over SSL.
• C、Implement Domain Security.
• D、Implement Secure/Multipurpose Internet Mail Extensions （S/MIME）.