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Exchange 2016 Troubleshooting: Event ID 9646 - Mapi session with client type MoMT exceeded the maximum of 32 objects of type Session

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In your Exchange 2016 environment, you might have noticed the following Event (Event ID 9646) being logged:

Mapi session (redacted) with client type MoMT exceeded the maximum of 32 objects of type Session

To resolve this issue, you can create a registry key on the server and then restart the Exchange Information Store.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeIS\ParametersSystem\Maximum Allowed Sessions Per User

The value for "Maximum Allowed Sessions Per User" Value data set to 500 and ensure it is set to a Decimal Value:

https://collaborationpro.com/wp-content/uploads/2018/09/ex2016IS.png

Once done, you can go to Services and restart the Exchange Information Store or reboot the server for the changes to take effect.