You have an Exchange Server 2010 Service Pack 1 (SP1) Edge Transport server named
Server1.
A partner organization has an Exchange Server 2010 SP1 Edge Transport server named
Server2.
You need to encrypt SMTP communication between Server1 and Server2. The solution must
ensure that both servers use a trusted certificate.
What should you do?

A.
Enable Externally Secured authentication.

B.
Enable Exchange Server authentication.

C.
Disable the Anonymous users permission group.

D.
Enable Domain Security authentication.

Explanation:
Exchange 2010 provides a feature set called Domain Security that provides administrators a
way to manage secure message paths with business partners over the Internet.
Domain Security relies on mutual Transport Layer Security (TLS) for authentication.
Successful mutual TLS authentication relies on a trusted, validated X.509 certificate chain
for the TLS certificates that are used for Domain Security.
Using PKI on the Edge Transport Server for Domain Security