To verify that your Exchange servers can resolve internal DNS names, you can use the DNS Resolver Tool (DNSDiag.exe) from Microsoft. Dnsdiag.exe is available for use on Exchange servers running Microsoft Windows Server™ 2003. This tool simulates the internal code path of the SMTP service and generates diagnostic messages that indicate how DNS resolution is proceeding.

Run DNS Resolver on the computer for which you want to verify DNS configuration. Your path should include %WINDIR%\System32\Inetsrv so that the tool works.

You can download the DNS Resolver tool from the Microsoft website (http://go.microsoft.com/fwlink/?LinkId=25097).
If you are running Exchange on Microsoft Windows® 2000, you can use the Nslookup tool to diagnose and troubleshoot DNS issues.

type dnsdiag –v 1 , verify that the output shows no errors. It probably will look like this

Created Async Query:
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QNAME = mail.fots.nl
Type = MX (0xf)
Flags = UDP default, TCP on truncation (0×0)
Protocol = UDP
DNS Servers: (DNS cache will not be used)
172.16.1.101
Connected to DNS 172.16.1.101 over UDP/IP.
Received DNS Response:
———————-
Error: 9501
Description: No records could be located for this name
These records were received:
fots.nl SOA (SOA records are not used by us)
Querying via DNSAPI:
——————–
QNAME = mail.fots.nl
Type = A (0×1)
Flags = DNS_QUERY_TREAT_AS_FQDN, (0×1000)
Protocol = Default UDP, TCP on truncation
Servers: (DNS cache will be used)
Default DNS servers on box.
Received DNS Response:
———————-
Error: 0
Description: Success
These records were received:
mail.fots.nl A 81.69.123.229
1 A record(s) found for mail.fots.nl
Target hostnames and IP addresses
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HostName: “mail.fots.nl”
81.69.123.229