> Kevin,
> The problem is server1 has a set of customers and server2 has a set of
> customers. Each server is auth for their respective customers.
> Customers on server2 can not reach customers on server1 and vice versa.
> I have logging on but can not see anything that's strange...

You don't think that getting FORMERR logged is strange?

> 04-Sep-2008 15:06:07.169 client query:
> mail.customer2.com IN A +
> 04-Sep-2008 15:06:07.169 createfetch: mail.customer2.com A
> 04-Sep-2008 15:06:07.170 client query:
> mail.customer2.com IN A +E
> 04-Sep-2008 15:06:07.170 FORMERR resolving 'mail.customer2.com/A/IN':

Make sure that you have your delegations correct. That if
a zone is delegated to a server that it is actually serving
that zone. That you get a SOA record returned in the ANSWER
section when you query the server with the zone name.

Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: Mark_Andrews@isc.org