If you can’t access a Mailbox with the following Error Message.

MAPI_E_FAILONEPROVIDER and Mailbox Permissions

Its most like the Mailbox Permisson for the Admin User is corrupted or false.
To set the a clean Permission:

  1. you need to open the Exchange Management Shell cmdlet and put the following Powershell code in (replace Domain with your Domain):

2. After this you set the permission new:

Now your Administrator has Full Access to the Mailbox.

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