You have an Exchange Server 2010 organization. A user named User1 connects to his mailbox using Microsoft Office Outlook. User1 reports that he is unable to send encrypted email messages to an external recipient named User2. You verify that User1 and User2 have email encryption certificates. You need to ensure that User1 can send encrypted email messages to User2. What should you do first?
A. Instruct User2 to add a delegate.
B. Instruct User2 to send a signed email message to User1.
C. Instruct User1 to send a signed email message to User2.
D. Instruct User1 to modify the sensitivity settings of the email message.