Full Access permission in outlook, but getting an error

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Hi @Payne, Wesley

May I ask how did you delegate the Full Access permission? Did you grant it in Exchange Admin Center or in the mailbox itself?

In your web mail of the account you want to access, click in the three-dot button > Sharing and Permission.

If you have full the Owner access here, you can only add the mailbox as a folder on your folder list.

If you want to open it using Open another mailbox, follow this article to grant the Full Access permission. You can also consider using PowerShell to perform this if you are familiar with it

If you have the correct setup, wait around 5-10 minutes. If the issue persists, you can try:

• Remove and re-add the permission.
• Using incognito web.
• Clear browser cache.

Please try and let me know how it goes.

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The error shown (AccessDenied / ErrorPermissionDenied / MapiExceptionNoAccess) indicates that, although the mailbox was added, the effective permissions in Exchange are not sufficient for Outlook on the web to create the required security context for that mailbox.

A similar behavior occurs when a user without a valid mailbox or without the correct access tries to work with a shared mailbox in Outlook on the web: Exchange cannot build the security context and throws an exception, resulting in an access/permission error.

To resolve this in Exchange Online:

1. Verify that the user account being used to open the mailbox has an active mailbox in Exchange Online (not disabled or terminated).
2. In Exchange admin center, confirm that this user has Full Access (and, if needed, Send As/Send on Behalf) permissions on the target mailbox.
3. If the user was recently granted Full Access, wait for permission replication (can take some time) and then sign out of all Outlook/OWA sessions and sign back in.
4. If the account previously had issues (for example, disabled mailbox), the tenant administrator should re‑enable or recreate the mailbox and then reassign the permissions before trying again.

If the problem persists after confirming the mailbox is enabled and Full Access is correctly assigned, the tenant administrator should open a support case with Microsoft, as this can indicate a backend issue similar to the documented security‑context problem.

References:

• Error message when a user who does not have a mailbox tries to move or delete an item that is in a shared mailbox by using Outlook Web App Premium