Domain resolution problem.

[Ali Eghtessadi]

I am having a problem resolving the domain "mailguard.nbb.co.jp" using
the internal dns servers in our network. The internal DNS servers are
unable to resolve it and then after a few days they can resolve this
domain again. This is causing the email flow between our offices to
fail. I also have a dns server which is outside the firewall and is the
primary for domain babcockbrown.com, this dns server can resolve the
mailguard.nbb.co.jp with no problem.

Any idea what the problem may be? I can provide a copy of our db file if
that helps. Please let me know and any help is very much appreciated.

Ali