MSExchangeMailboxAssistants event 4999

MS Windows 2019, MS Exchange 2019 CU7

MS Windows and MS Exchange are installed with Russian. An attempt was made to switch the Windows interface to English, after which the MSExchangeMailboxAssistants service starts with an error and stops. I tried to return the Windows interface language back to Russian, but the service error remained.

Thanks for any help.

Error text:
Watson report about to be sent for process id: 26956, with parameters: E12IIS, c-RTL-AMD64, 15.02.0721.008, MSExchangeMailboxAssistants, M.Exchange.Assistants, M.E.A.AssistantsRpcServer.RegisterAssistant, System.ArgumentException, 503a-dumptidset, 15.02.0721.008.
ErrorReportingEnabled: False

Accepted answer

Максим Хирьянов 96 Reputation points

2021-03-29T16:11:04.017+00:00

Everything was decided by installing CU8. The service MSExchangeMailboxAssistants is working normally, there are no errors.
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Lucas Liu-MSFT 6,161 Reputation points

2021-03-30T06:20:25.797+00:00

Hi @Максим Хирьянов ,
I am glad to hear that this issue have been solved. Thanks for you sharing the solution.
You can mark the solution as an answer when you are free, which can help more people who have the same issue.

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1 additional answer

Lucas Liu-MSFT 6,161 Reputation points

2021-03-10T05:16:12.143+00:00
Hi @Максим Хирьянов ,
Are there any Exchange functions that are not working properly?
Does any specific error pop up when you start the MS Exchange Mailbox Assistant service?
Do you try to restart the Exchange server and MSExchange Mailbox Assistants service? If not, please try.
1.1.Please run the following command to make sure that all required service are running:

Test-ServiceHealth

2.According to the error information, we could only know that Microsoft Exchange Assistants service failed. It may not be possible to know the root cause of the error, so please check if there are any related errors in the event log, or if there are any errors in Exchange. Please share the information with us, but please pay attention to covering your personal information.

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Максим Хирьянов 96 Reputation points

2021-03-11T05:56:06.073+00:00

In order

Mail approval does not work. A letter comes for approval, you press "approve", but the letter is not delivered to the addressee.

When starting the service MSExchangeMailboxAssistants, an error appears with the number 4999, source "MSExchange Common" and the text:

Watson report about to be sent for process id: 26956, with parameters: E12IIS, c-RTL-AMD64, 15.02.0721.008, MSExchangeMailboxAssistants, M.Exchange.Assistants, M.E.A.AssistantsRpcServer.RegisterAssistant, System.ArgumentException, 503a-dumptidset, 15.02.0721.008. ErrorReportingEnabled: False

Restarting the service. Restarting the server. The error remains.

Test-ServiceHealth

Once again, I want to clarify that the service starts and stops immediately with error 4999 and so on forever

I beg your pardon for my english, google translate

Lucas Liu-MSFT 6,161 Reputation points

2021-03-15T09:38:49.287+00:00

Hi @Максим Хирьянов ,
Please run the following command to check if the arbitration mailbox is complete.

Get-mailbox -arbitration

Please try to run the following command to moving the arbitration mailbox to another mailbox database. Then try to restart MSExchangeMailboxAssistants service again.

Get-mailbox -arbitration | New-moverequest -targetdatabase <DBName>

As mentioned above, we could only know that Microsoft Exchange Assistants service failed from Event ID 4999. Please try to restart the MSExchangeMailboxAssistants again and see if there have any other related error logs in the Event Viewer.

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Lucas Liu-MSFT 6,161 Reputation points

2021-03-18T08:41:42.32+00:00

Hi @Азер Мирзоев ,
Do suggestions above help? If the issue has been resolved, please click “Accept as answer” to mark helpful reply as an answer, this will make answer searching in the forum easier and be beneficial to other community members as well.

Thanks for your understanding.

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Максим Хирьянов 96 Reputation points

2021-03-18T12:24:40.073+00:00

Sorry for the long silence.

Get-mailbox -arbitration

Get-mailbox -arbitration | New-moverequest -targetdatabase <DBName>
I will do this on 03/26/2021.

Thank you for your help.

Lucas Liu-MSFT 6,161 Reputation points

2021-03-23T07:54:53.323+00:00

Hi @Максим Хирьянов ，
Ok, looking forward to your feedback.

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