Is there any authentication performed when one Exchange server talks to another through SMTP?
In Exchange 5.5, server-to-server communication is authenticated and encrypted using system-level Remote Procedure Call (RPC). With Exchange 2000, each server uses SMTP authentication with Kerberos. Encryption is not done by default. There are two options for encryption—Internet Protocol Security (IPsec), which is built into Windows 2000, and Transport Layer Security (TLS), built into the SMTP service and used by Exchange 2000. TLS is also known as secure sockets layer (SSL).
