Trying to setup an Exchange 2013 server, with the DC and Exchange on same machine. WHen I try to deliver for either of the 2 mailboxes I have setup, I get this error.

The server returned status code 451 - Error in processing. The server response was: 4.7.0 Temporary server error. Please try again later. PRX3 

It doesn't seem to be a resource issue (I'm running an XL instance on Azure), and all other connectivity works fine (and fast). I just can't receive email there. 

Looking in the event logs, I saw one issue related to the Front End HTTP proxy, but I wouldn't assume that's relevant here. (And connectivity via Outlook & OWA seem to be fine, with the exception of some redirect issues on the latter).

I did end up installing Exchange on a secondary drive for space considerations, so the location is different... not sure if that would factor in either.

Any ideas? I don't even really know where to start debugging this. I'm trying to set this up to work on some event sync/forwarding code.

Ok, I think I solved my problem but figured I would update here for others who may be running into the same issue.

In my \Exchange\TransportRoles\Logs\FrontEnd\ProtocolLog\SmtpReceive\*.LOG, I found more detailed information on the issue.

"Message or connection acked with status Retry and response 
451 4.4.0 Error encountered while communicating with primary target IP address: ""421 4.2.1 Unable to connect."" 
Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts. The last endpoint attempted was 10.10.10.1:2525"

I thought creating an endpoint for 25 would be sufficient, but once I created another endpoint for 2525 then my tests started working.

Hi

Thanks for sharing your solution, please Mark your post As Answer to finish this thread

Cheers