Unable to open default folders-you do not have permissions to logon error when accessing another user's mailbox folder

Original KB number:   2796317

Symptoms

A Microsoft 365 user tries to open another user's Microsoft Outlook mailbox folder to which the user was granted access. However, the mailbox folder doesn't open. Instead, the user receives the following error message:

Unable to open default folders-you do not have permissions to logon

This issue occurs if the user doesn't have sufficient permissions to access the mailbox folder.

Resolution

When a user wants to give another person access to one of their own mailbox folders in Outlook, the user has to grant the other person access to the specific folder that the user wants to share and also to all other parent folders in the folder hierarchy. It's not enough for the user to grant permissions only to the specific folder that they want to share.

For example, user B wants to grant user A access to the Invoices folder, and the Invoices folder is a subfolder of the user's Inbox folder. To grant this access, user B has to grant permissions to user A for the following folders in Outlook:

• The Invoices subfolder
• The Inbox folder
• The parent Mailbox folder

For more information about how to set up mailbox permissions in Outlook, see Allow someone else to manage your mail and calendar.

For more information about how to manage another user's mailbox data in your Outlook profile, see Manage another person's mail and calendar items.

More information

In Microsoft 365, Exchange Online admins can also grant mailbox folder permissions by using Exchange Online PowerShell. The Add-MailboxFolderPermission cmdlet can be used to grant access to specific folders in a user's mailbox. For more information about how to use this cmdlet, see Add-MailboxFolderPermission.

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