Permission & Access Issues

How to Give One Shared Mailbox Access to Another in Microsoft 365

Huda Qurayshi Oct 26, 2026 868 views

Question details

The user needs to grant full access permissions from one shared mailbox to another, as the standard Microsoft 365 portal lacks a direct GUI option for this specific configuration.

How to Give One Shared Mailbox Access to Another in Microsoft 365

Product: Microsoft 365 / Exchange Online
Device & OS: not provided
Scenario: Assigning delegate or full access rights between two different shared mailboxes.
Observed behavior: The Microsoft 365 portal does not display the usual option to configure these specific access permissions, preventing the user from completing the task via the web interface.

Before you start

Ensure you have Exchange Administrator privileges in your Microsoft 365 tenant and that the Exchange Online PowerShell V3 module is installed on your computer.

Solution 1Recommended

Grant Shared Mailbox Access via Exchange Online PowerShell

Since the Microsoft 365 admin center GUI does not support adding a shared mailbox as a delegate to another shared mailbox, you must use PowerShell to assign the permission.

Using the Add-MailboxPermission cmdlet allows administrators to explicitly define access rights bypassing the limitations of the web portal's interface.

Open PowerShell

Right-click the Start button on your Windows computer and select 'Windows PowerShell (Admin)' to run the terminal with elevated privileges.

Connect to Exchange Online

Type the command 'Connect-ExchangeOnline' and press Enter. A sign-in window will appear; authenticate using your Microsoft 365 admin credentials.

Execute the Permission Command

Run the following command: Add-MailboxPermission -Identity "shared1" -User shared2 -AccessRights FullAccess -InheritanceType All

Replace Placeholder Names

Before pressing Enter, make sure to replace 'shared1' with the exact email address or alias of the target mailbox, and 'shared2' with the mailbox that needs to be granted access.

Grant Shared Mailbox Access via Exchange Online PowerShell

Propagation Delay: It can take up to 60 minutes for the new mailbox permissions to fully propagate across Microsoft 365 servers and take effect in Outlook.

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Frequently Asked Questions

Can I add shared mailbox permissions via the Microsoft 365 Admin Center?

You can easily add regular user mailboxes as delegates to a shared mailbox in the Admin Center. However, adding another shared mailbox as a delegate often hides the option, requiring you to use Exchange Online PowerShell.

How long does it take for mailbox permissions to apply after running the PowerShell command?

After granting permissions via Exchange Online PowerShell, it typically takes anywhere from 15 to 60 minutes for the changes to fully sync and take effect in Microsoft 365 and Outlook clients.

What level of access does the FullAccess parameter grant?

The FullAccess right allows the delegated shared mailbox to open the target mailbox, view, create, and manage its contents exactly as if they were the primary owner of that mailbox.

Document & File Issues