You have an Exchange Server 2010 organization.A user named User1 connects to his mailbox by using Microsoft Office Outlook.User1 reports that he is unable to send encrypted e-mail messages to an external recipient named User2.You verify that User1 and User2 have e-mail encryption certificates.You need to ensure that User1 can send encrypted e-mail messages to User2.What should you do first？（）

• A、Instruct User2 to add a delegate
• B、Instruct User2 to send a signed e-mail message to User1.
• C、Instruct User1 to send a signed e-mail message to User2.
• D、Instruct User1 to modify the sensitivity settings of the e-mail message