Restarting Domain Controllers causing NDR's from Exchange servers

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?
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how many global catalogs do you have?
deshawAuthor Commented:
I have two DC's in my site which are GC's as well
deshawAuthor Commented:
Do you have any thing to share on this issue or this can be deleted instead of keeping it as open question
Hypercat (Deb)Commented:
I don't think the global catalog is the issue, since this is only used by the RUS.  Rather, it is more likely a DNS issue or user authentication issue.  Have you seen any event log errors in your FRS or DS logs?  Maybe try running a DCDIAG on both DCs and see if there are any errors.  You could also check the replication status using REPLMON (in the Windows Support Tools) to make sure that both DCs are operating properly. It also might be DNS-related.  Does your Exchange server have both DCs listed as DNS servers? Is your DNS AD-integrated? Is the Exchange server by any chance using a smart host or DNS setting on the SMTP virtual server that might be affecting this behavior?

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Windows Server 2003

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