Hi @X-Box-11-2021 ,
First of all, I would like to confirm how long ago the permissions were removed, because based on my experience, sometimes it may take up to 72 hours to take effect. And if it is less than the above time, you can wait again for some more time and see if there would be any difference. If it has been more than three days, I can understand that you’ve already checked the access permission, but it’s still recommended to double confirm it by running the Get-MailboxPermisson cmdlet like below, ensuring that the permission of this user has indeed been removed.
Get-MailboxPermission -Identity <MailboxIdentity> -User <UserIdentity>
If the above check shows that there is no permission and the user’s account is configured as Exchange cached mode, you can try switching to Exchange online mode and check the result.
If the issue still persists, I’d recommend re-adding the full access permission to the user again and remove them again. Below are the basic steps for your reference:
1 - Connect to Exchange Online PowerShell.
2 - Run the following command to provide full access and disable automatic mapping.
Add-MailboxPermission -Identity <MailboxIdentity> -User <UserIdentity> -AccessRights FullAccess -AutoMapping $false
3 - After running the previous command, remove full access to the user's mailbox again.
Remove-MailboxPermission -Identity <MailboxIdentity> -User <UserIdentity> -AccessRights FullAccess
For more information, see remove automapping for a shared mailbox in Outlook.
Usually, the auto-mapped mailbox can be successfully removed through the above steps. (As mentioned before, there may also be delays.)
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