Hi @-- -- ,
Based on the search, the problem may be Exchange Trusted Subsystem is not granted the "modify permissions" permission. Please follow these steps to ensure Exchange Trusted Substystem has the required permissions:
• Open Active Directory Users and Computers.
• Click View, and then click Advanced Features.
• Right-click the OU that contains the user and then click Properties.
• In the Security tab, click Advanced.
• In the Permissions tab, click Add.
• In the Enter object name to select box, type Exchange trusted subsystem, and then click OK.
• In the Object tab, select This object and all descendant’s objects in the Apply onto list, locate Modify Permissions in the Permissions list, and then set it to Allow.
• Click OK
• Make sure above option is checked on all OU’S listed in the object path of the user object
For details, please refer to the documentation:
You can also try other troubleshooting steps from this article:
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