I am not an exchange administrator if there's a more appropriate place for this question please suggest it and accept my apology.I work for a company doing IPAM software, a reseller of ours has a large installation where his users report that if the Exchange servers primary DNS server is not resolving (but on line) the Exchange server will patiently wait, doing nothing. But if the Exchange servers primary DNS server is off line (literally if they unplug DNS1 from the network), it will then use it's secondary DNS server. This is unique in my experience and I wonder if this is a controllable behaviour on the Exchange server (anyplace I can "read more about it"... w/out becoming an Exchange admin?) Normally, DNS clients time out waiting for a DNS response and transparently use the second DNS server they're configured with. -Boyd

let's iron out what you mean by "not resolving (but online)" mainly the not resolving part. Not resolving would mean the a DNS request was made and the primary DNS server didn't have a record for it. This and any DNS request stops here, everyday. The DNS request will not go to a secondary DNS server if it was given back a response of no record found. Now if the primary DNS server is busy and never gives a response to the request then it will time out and request again from the secondary DNS server. Exchange is no different in how it requests from DNS. If Exchange makes a DNS request and there is no record it responds to that request with no record found. If Exchange doesn't get a response back it will re-request from a secondary DNS server quickly.This really sounds like a misconfigured DNS. If these are internal DNS requests, you should verify that a valid A record has been created. If these are external DNS requests you should make sure that the internal DNS server is properly setup for zone transfers from your ISP's DNS server and set to query an external DNS server if there is no record found on your internal DNS servers. I would also look at the utilization of the "DNS1" server, if it is accepting DNS requests and is unable to fulfill them timely there is probably something else going on.Todd Seagraves