Exchange 2007

Last night, we swapped ISPs. We updated DNS records. Emails are coming through. However, when we try to send to 'some' people, the message gets placed in the Exchange queue with a message 451 4.4.0 Primary Target IP address responded with 421...temporarily rejected. Reverse DNS (for new IP) Failed.
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Scot HalvorsenCommented:
Mailservers usually require that their IP address also have a PTR (or reverse pointer) record. Most likely your previous ISP supplied reverse record, but your new one does not.

You can check this by issuing the following command for both IP addresses and see if this is correct;

C:/> nslookup <ipaddr>

Open in new window

An example of a succesful query;

C:/> nslookup
Server:  UnKnown

Non-authoritative answer:
Addresses:  2607:f8b0:4005:801::200e


C:\> nslookup
Server:  UnKnown


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As you can see, reverse records do not need to match.

If you find that your new IP address does not have a reverse record, you will need to work with them to create it.

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CBurch22Author Commented:
Thank you! Solved the problem.
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