I'm having a problem with a new Exchange 2013 CU7 server on Windows Server 2012 R2. Having intermittent 451 4.7.1 Temporary server error. Please try again later PRX2 on receiving mail on connectors configured with port 25. I keep thinking I have solved the issue. If I think I fix it in the morning, it works all afternoon. The next day I'm getting the error again. It is driving me and my client nuts!
The Exchange server has the DNS servers for the internal DC's set in EAC for both internal and external lookups.
The DC's have DNS set to forward to external DNS servers. I 'm having no issues with DNS resolution anywhere in the environment.
The Exchange server is able to resolve internal and external DNS.
One thing of note and I'm not sure if this is normal, if I ping the DC's i get back IPv6 address, never an IP4. I have even set the servers in a host file.
Thankfully I have a filtered mail service that will spool mail if it cannot connect to the mail server and retires at set intervals. So I have not lost any emails.
There is no filtering or AV scanning happening on the server or Exchange level.
Nothing in the event logs of note related to this issue.
At the moment it is working, but I'm sure it's going to stop again soon.
