Bind 9 configuration

[Stayvoid]

>> 3. I have joe.example.com in db.example.com. Will it be my email address (e.g. joe at example.com)?
>The domain name joe.example.com doesn't correlate to the mailbox joe at example.com. You have specified your
>mail exchanger as mail.example.com. That host needs to know how to deliver messages to the mailbox
>joe at example.com.

Could you be more specific?
How to make it work?