When running your own DNS name server, it is well advised that you add MX (mail exchanger) records to your domains.
Otherwise, you'll notice that all of a sudden, nobody seems to send you mail any more.
It is also well advised that once you realize that your MX records are nonexistent that you do not simply point them to your server using the internal IP address. For some odd reason, 192.168 addresses won't route across the Intertubes.
*grumble*