In Exchange 2013 RTM and Exchange 2013 CU1 you may occasionally receive the following errors in your Outlook clients as seen below.

<strong>451 4.7.0 Temporary server error. Please try again later. PRX5</strong>
And in the connectivity logs you may see
NS server returned ErrorRetry reported by 0.0.0.0. [Domain:Result] = server.domain.com:ErrorRetry
(The DNS query for  'Undefined':'internalproxy':'00000000-0000-0000-0000-000000000000' failed with error : ErrorRetry)

This is currently a know problem with Exchange 2013 and can be resolved with the following. By default the standard frontend receive connector is bound to all addresses on the server as seen below, this is now know to occasionally cause issues with DNS lookups.

We need to change the setting here to the specific IP address that the Exchange 2013 server uses and also put a line in our hosts file. To edit the bindings in Exchange 2013 click the pencil sign above to edit and change the ip address to the Exchange servers NIC as seen below.

Once done apply all settings. Now browse to the hosts file that is located in C:>Windows>System32>Drivers>etc

Edit the host file and add entry’s for your Exchange 2013s IP and its host name, for example.

192.168.16.1 server
192.168.16.1 server.domain.local

As seen here. Then reboot your server and you will not receive the Exchange 2013 451 4.7.0 Temporary server error. Please try again later. PRX5 error.

Note if this post does not resolve your issue please check this one https://wp.me/p2Lmvg-7r

thanks to Allen White on. Posted in Exchange 2013