Using x.com on LAN when authoritative NS on inet

[Kevin Darcy]

hobosalesman at gmail.com wrote:
> 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?
>   
You don't really have much of a choice here, since MX records apply to 
the "domain" part of a mail address (everything after the @-sign). You 
can't use MX'es to redirect individual mailboxes to different destinations.

So, you'll need to point the x.com MX record at some mail server that 
looks at the mailbox part of the address and forwards and/or delivers 
accordingly. How you set up a mail server to do that is off-topic for 
this list, and dependent on what mail software you use. I know for 
sendmail you could just use an alias file. But you should probably ask 
on a list that's specific to whatever software you use.

                                                                         
               - Kevin