Using x.com on LAN when authoritative NS on inet

[hobosalesman at gmail.com]

I'm trying to use x.com (I own the domain) on my LAN. I pay a company
to host x.com (web/mail). I've set up bind9 on my LAN and made it
authoritative for x.com, set up DNS for all my hosts in this domain. I
can resolve x.com to my host's IP so the website works, but mail has me
confused, I'm not so familiar with MX records or MDA/MTAs. I want to
have mail for *@x.com sent to the mail server on my LAN, except for a
few addresses. I need to mail bob at x.com from within the LAN and have it
reach my host's mail server so bob can read it.

My bright idea is to send all mail from within the LAN to the LAN mail
server, and have it forward specific addresses to my host's server. I
haven't confirmed this is possible, I'm looking for someone to maybe
point a finger in the right direction?