Exchange 2019 SMTP random delays of 1 minute when sending email

Copper Contributor



We recently moved from a 3 server Exchange 2016 DAG to a single Exchange 2019 server.  We are in a hybrid set up, all mailboxes in Exchange Online, mainly using the on-prem Exchange Server for SMTP and user management.  When we had the DAG, we also had a load balancer in the setup.  We've since taken that out and changed all DNS to point to the IP of the new 2019 Exchange Server.


Everything seems to be running fine except we have a lot of on-prem apps and printers that use SMTP to send email.  We are facing an issue where most emails have a delay of 1 minute and a few seconds, which causes the page where a user submits the email to wait for a response and just sits there for that minute.  In some instances, our SQL jobs see this as a failure and retry, but then we get duplicate emails for those task notifications.


Sometimes it is working fine, I can send 10 emails from a printer in a row with no delay then the 11th has the delay.  I've worked with Microsoft to check settings and logs and they are indicating it is related to a networking problem but the delay is on the server itself when I analyze the message header of a delayed message as seen in the image (blacked out hostname of Exchange server).  Next step in the message analyzer is from our public IP to Exchange Online which has no delays.




Any guidance would be appreciated.

5 Replies
There a re a number of different resources required on the Exchange server to send a messages. It will need adequate CPU and memory to process the messages, but it also needs to write the message to disk at different points in the transport pipe. Look at any resource constraints there.

Exchange then has to initiate a connection to the next hop mail system (I'd assume that's Exchange Online here) to send the message on, so it could be on that network path where the delay is.

@Dan_Snape it should have plenty of resources (6 core CPU, 32 GB RAM, health checker suggests 128 GB but that seems overkill to me) to handle the email.  It is not handling a ton of email, less than 100 messages per hour.  I am reluctant to think it is the network, as the network is not changing and at one point in the day, email moves quickly and at other times it takes that 1 minute delay for every message.

What about disk utilisation, including any virus scanning or other security products that might lock files?

@Dan_Snape Hi Dan, we have Symantec antivirus on it but doesn't appear to be an issue (we had it on all of our old 2016 servers as well).


Did many tests on Friday and found no delays.  Similar this morning but got one delay but right after the next few went fine.

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