Friday, June 17, 2016

Temporary Server Error and HOSTS file

Hi folks,

Just wanted to share with you about yet another adventure I faced. When some of the application servers that were configured to use my Exchange 2013 servers farm behind the load balancer attempted to send email via them they were prensented with the following error:

451 4.7.0 Temporary server error. Please try again later. PRX5 Downstream

As I was talking to my older brother Google when investigating this issue all the articles including this one from Dell were pointing to the known bug with the Exchange 2013. Recommendations were to update receive connectors to listen on the primary IP address of the NIC and also update HOSTS file to include IP addresses of Exchange server there.

I personally haven't got to that point because I was more lucky. When I edited HOSTS file I found there weird IP addresses (outside of my IP address range) and Exchange servers' hostnames next to them. I removed all incorrect records from the HOSTS file and rebooted the server after which my applications were able to use SMTP on Exchange to send messages.

Therefore my advise if you have this error first check your HOSTS file for strange records before you try any further troubleshooting.