When I restart any of Domain controllers in my site, Exchange server is generating NDR's with "smtp;550 5.7.1". AFAIK, exchange 2003 should be intelligent enough to wait for a failed DC for sometime and switch over to another DC. But it is not happening in my case, when ever I reboot one DC, exchange is throwing NDR's for mails which came for processing at that time. And after few mins it is not generating NDR's for further mails. All the DCs in my site are GCs.
Any one have idea why it is happening this way?