I have question regarding encryption of email messages from a end user to receiver user.
Putting SSL on exchange server, it encrypts message traffic from a client to the server and either way. What about the SMTP traffic between the server to the receiver's SMTP server and from the receiver SMTP server to the receiver's interface?
sender--------sending SMTP server--------Internet---------receiving SMTP server----receiver
In this case, I put SSL on my Microsoft exchange server between sender and the sending SMTP server. So it encrypts the message. When the message leaves the sendng SMTP server and during the trip to the receiing SMTP server, how does the message decides what encryption to choose and how can I choose it and deploy?
Even when the sending SMTP server enfoce the high encryption method, if the receiving SMTP server doesn't have the encryption method, then how the two servers negotiate the encryption to use?