What do you think he would say in his disclaimer and what about that would offend you? Is it because it would be a reminder that the communication was professional and not personal?

My T's disclaimer reads: This is a private message. If you are not the intended recipient, please notify the sender and then delete this message.

I am not offended by it. It just reminds me that email communications can sometimes go astray and nothing by email is ever really private. It's a risk we take for the convenience of communicating this way. I appreciate having that convenience! If I don't want to take this risk, I can insist all of our communications be by phone.