From: "Vince Van De Coevering" <vpv at figaros dot com>

> Or take the easy road and swap DNS hosting with someone else...

> Zone transfers can be encrypted, password protected, and restricted by IP
> address.
> BIND will notify slave servers when the domain has changed.

I second this.  Additionally if a mailserver is down, a sending mail 
programs may handle it different than a mailserver with a failed DNS query. 
You may loose more mail the other way.

                        Lee