Distribution list expansion cause high cpu usage Exchange

Question

We observed that cpu usage can spike to 100% when our event-mailbox sends out Calendar Invitations with multiple distribution-lists and recipients (Over 8000 recipients). They usually use Outlook and copy paste all recipients and dl`s (about 9000 recipient) in to an calendar invitation. This caused 37min performance issues, like this: Our Server Setup:: active/ passive dag 8x Exchange 2016 servers with 6 cpu/ 64 GB / 15000 mailboxes running latest CU16, OS patches Outlook 2010/2016 in cached mode and online Organization TransporConfig: ![43484-image.png][1] Incoming service desk Incidents (37min): · Outlook Online Freeze · Delayed Mail Delivery · Outlook could not start Exchange 2016 100% CPU Usage (38min): VMA1 100% CPU and not responding (10:48-11:10Uhr) VMA2 100% CPU and not responding (10:48-11:10Uhr) VMA3 100% CPU and not responding (10:48-11:10Uhr) VMA4 100% CPU and not responding (10:48-11:10Uhr) (FailOver has been performed) Exchange 2016 63% CPU Usage (15min): VMP1 63% CPU 10:55-11:10Uhr Network OK VMP2 63% CPU 10:55-11:10Uhr Network OK VMP3 63% CPU 10:55-11:10Uhr Network OK VMP4 63% CPU 11:00-11:10Uhr Network OK I’m wondering if anyone has seen this before with exchange 2016 and if there is a setting to prevent it. Even when server did the expansion, email was sent to a dl, cpu goes back to same high usage condition and outlook was locked for up to 15 min. Thanks in advance

Answer 1

Hi anonymous user,

We observed that cpu usage can spike to 100% when our event-mailbox sends out Calendar Invitations with multiple distribution-lists and recipients (Over 8000 recipients).

Is this a recently occurred issue? If so, have you made any changes to your Exchange environment before the issue started?
Does it affect meeting invitations sent to less distribution-lists and recipients, like 1000 recipients?
What about sending a normal message rather than a meeting request, will it case the same high CPU usage?

Given current situation, I'd like to suggest having a check via the Event Viewer and see if there would be any relevant events recorded. Besides, have you installed any third party applications like anti-malware on the Exchange server? If yes, it's recommended to temporarily disable them to help narrow down the problem.

Furthermore, the latest build for Exchange 2016 is now CU18, you may consider upgrading to the latest version to see if there would be any improvement.

---

If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Answer 2

Is this a recently occurred issue? If so, have you made any changes to your Exchange environment before the issue started?
AW: No changes.. It's a new Exchange environment, which we are migrating to.

Does it affect meeting invitations sent to less distribution-lists and recipients, like 1000 recipients?
AW: Not sure.. But we did not experience it before. Less is not a problem.

What about sending a normal message rather than a meeting request, will it case the same high CPU usage?
AW: We have no issue with emails sent to multiple members bin in groups.

Given current situation, I'd like to suggest having a check via the Event Viewer and see if there would be any relevant events recorded.
AW: No backpressure and other events that explain this behavior.

Besides, have you installed any third party applications like anti-malware on the Exchange server? If yes, it's recommended to temporarily disable them to help narrow down the problem.
AW: Only Antivirus (TrendMicro)-

Furthermore, the latest build for Exchange 2016 is now CU18, you may consider upgrading to the latest version to see if there would be any improvement.
AW: Not Possible at the moment.

Thank you for your suggestions..