How to hide mail id in the title bar of chat window?

There's no way to hide your mail id in the title bar of the chat window.

But I suggest that you should create a "fake profile":

1. After logging in: Messenger -%26gt; My profiles

2. Create/edit my profile

3. Fill in the blanks

4. Finish

5. Log out

6. Log in

7. Messenger -%26gt; My profiles

8. Activate that "fake profile" you've just created.

In the other way: Don't let any one add you in their messenger list.