Hi everyone
We recently upgraded our two Exchange 2013 servers to CU12, but since then we have had some issues with incoming external mail being delayed. Our Exchange setup is below:
MailServer1 - CAS & mailbox
MailServer2 - mailbox
Our public DNS points to our CAS server through a firewall so all external mail is routed to the CAS server. Before reaching the firewall, mail goes through a McAfee smart host. Since the upgrade to CU12 we've noticed a large number of e-mails stopping at the smart host with the error:
4.7.0 Temporary server error. Please try again later. PRX4
The e-mails keep trying to send and eventually get through, but this is causing some external e-mails to be delayed by up to 2 hours.
I have checked the submission logs (Exchange Server\V15\TransportRoles\Logs\Mailbox\Connectivity\Submission) on the CAS server and this error also appears a number of times here. Another strange thing is that when mail is accepted from the smart host it only shows MailServer2 as the responding server on the McAfee portal, whereas before the CU12 upgrade either of the 2 could respond.
I've checked the event logs on both mail servers and the only errors shown on there relate to performance counters not being loaded, which I don't think is related. When I check the queues on the two mail servers, only a submission queue is shown on MailServer1, where MailServer2 shows a "SmartHostConnectorDelivery" queue and "SMTP Delivery to Mailbox" queues. I'm sure that prior to the CU12 upgrade these extra queues were on MailServer1 rather than 2.
I'm not quite sure where to go from here as mail is working generally but the external email delays are becoming a problem. I'd be grateful if someone could let me know of anything that may have caused this problem, and whether anyone else has experienced similar issues after upgrading to CU12?
Thanks for your help in advance.