Forward Error PRX5

Question / Problem

What can I do if the Exchange Server responds: "451 4.7.0 Temporary server error. Please try again later. PRX5"?

Answer / Solution

This error results of invalid DNS settings. To solve it add the local server's IP to our hosts file (C:\Windows\System32\drivers\etc\hosts):
 192.168.1.5 server
 192.168.1.5 server.domain.local
Then restart "Microsoft Frontend Transport" and "Microsoft Exchange Transport" services.