there is a list archive for BIND/DNS at:
http://www.isc.org/ml-archives/bind-users/
ALso on there you can join the list, which is a crossover to the newsgroup:
comp.protocols.dns.bind (i think that is what it's called).
As for the MX record. The MX record is what tells the world to send mail to
the domain being resolved, which you already know. You may be able to ping
it, but can you see it via nslookup (on a 'NIX machine).
First, if you do a NSLOOKUP and it says "non-authoritive answer", then it's
cached in your DNS and won't be able to truly test the outside availability.
The best way to tell if ppl can see it is find a UNIX box, and do the
following (or email me directly, and I'll look it up):
nslookup
>set type=mx
>mail.xyz.com
and see what it gives you. Personally, I would make sure it's in the zone
file of my serving DNS machines. It's only 1-2 lines in the zone files and
may save future headaches down the road.
Just my $.02 worth.
Izzie