Forward Error PRX2

Question / Problem

What can I do if the Exchange Server responds: "451 4.7.0 Temporary server error. Please try again later. PRX2"?

Answer / Solution

This error may occur if you only have 1 domain controller and put a router as secondary DNS server on all configurations.
Simply remove the secondary DNS which does not point to the internal DNS/Domain Controller.
Forwarding typically would be handled by the DNS servers in your environment, so a secondary public DNS would not be configured in a typical production environment.

If this does not correct the error, try to create a reverse lookup zone on the DNS server.