dns and mail setting

[Phil]

I am triing to set up my DNS server, running RH 6.1 & Bind, so that my mail
server can receive mail at user at mydomain.com but I can only get my mail
server to receive mail at  user at host.mydomain.com.  In the zone file I have
a MX record of  host.mydomain.com.  What do I have to have in my DNS server
for my mail server to receive mail in the user at mydomain.com format.

thanks