Re: [exim] DNS Question - Advanced

I have another tricky DNS question. I'm scream testing my new dnsbl
server and I'm going to open it up for others to use soon. Just working
out the final details.

So - here's my tricky question. I have 2 DNS servers. Server A runs
MyDNS - a MySQL driven server. It's the one that does the work behind
the scenes. It has no caching and should be considered to be slow.

Server B is a regular DNS server set up for caching and running BIND.
It's the one that will be the public face for the blacklist providing
caching for Server A so as not to load down Server A.

So what I want is that Server B secretly knows where Server A is so that
any request of dnsbl.junkemailfilter.com goes to Server B and Server B
passes the request on to Server A and caches it reducing the load on
Server A and keeling it hidden from the world.

So - how do I do that? What do I put in named.conf to tell it to route
certain requests to a Server A?

Thanks in advance.