Internal Mailflow Intermittent

Joel Henderson 6

Good morning,

I have an Exchange environment with an Edge Transport server running 2019 and two Mailbox servers running 2016 CU21 that are both part of a DAG. The DAG was a new install and mailflow was functioning correctly for about 3-4 days, but then mail has started not delivering intermittently. I did notice that one of the queues on the new Mailbox server for Submission has over 13,000 emails in it.

I have tried to make sure the licensing is correct and the receive connectors are correct, but the issue persists.

Any help would be greatly appreciated.

Kael Yao-MSFT 37,491 Reputation points Microsoft Vendor

2021-09-21T06:57:22.137+00:00

Hi @Joel Henderson

Does this issue occur after you install the new mailbox server into the environment?

Can you find some error or warning events logged in the event viewer>application log on the new Mailbox server?
For example, event 15004-15007.
If any, it may indicates the server is having back pressure problems.

Please also try restarting the Microsoft Exchange Transport service on the new Mailbox server and see if the messages would leave the queue.

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Joel Henderson 6 Reputation points

2021-09-21T19:44:51.78+00:00

II have tried a few times to restart the Transport service. I see that the messages are indictating deferred by categorized agent.
Kael Yao-MSFT 37,491 Reputation points Microsoft Vendor

2021-09-22T07:26:17.597+00:00

Hi,
Thanks for the update.
I suppose it may be caused by back pressure.

Please have a check if there are related events in the application log.

1 answer

Joel Henderson 6 Reputation points

2021-09-22T15:23:49.253+00:00

The issue was the Malware Agent on the new mailbox server. Once that Transport Agent was disabled and the Transport service was restarted, mail started to flow out of the backlogged queue.
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1 person found this answer helpful.
Kael Yao-MSFT 37,491 Reputation points Microsoft Vendor

2021-09-23T00:00:38.303+00:00

Glad to hear the issue has been resolved.
Thanks for the sharing.

Please feel free to mark your reply as the answer to the question.
It would be helpful to other community members.
Thanks for your understanding.

Kael Yao-MSFT 37,491 Reputation points Microsoft Vendor

2021-09-27T08:07:11.823+00:00

Hi @Joel Henderson

If the issue has been resolved, please feel free to mark your reply as the answer to the question.
It will highlight the answer and be helpful to other community members.
Thanks for your sharing.
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