How to Give Mailbox Permissions in Office 365

Updated 14 November 2026 · Standard formula, shown below

This guide shows you how to grant another user access to a mailbox in Microsoft 365 (formerly Office 365). You can give someone full access (open and read everything), send-as permission (send email that appears to come from that mailbox), or send-on-behalf permission. You’ll need to be a global admin or an Exchange admin in your organization to make these changes.

What You’ll Need

Global admin or Exchange admin role in Microsoft 365
Access to the Microsoft 365 admin center (admin.microsoft.com)
The email address of the mailbox you’re granting access to
The email address of the user who will receive the permission

Step-by-Step

Sign in to the Microsoft 365 admin center. Go to admin.microsoft.com and sign in with your admin account.
Navigate to Exchange admin center. In the left navigation, expand Admin centers and select Exchange. This opens the Exchange admin center (EAC) in a new tab.
Go to Recipients > Mailboxes. In the EAC, select Recipients in the left menu, then click Mailboxes.
Select the target mailbox. Find and click the mailbox you want to grant access to. A details pane will open on the right.
Open mailbox permissions. In the details pane, scroll down and click Manage mailbox permissions under “Mailbox permissions.”
Add a user for Full Access. To give full access (read, create, delete items), click Add permissions next to “Full Access.” Search for and select the user, then click Save.
Add a user for Send As. To let a user send email that appears to come from this mailbox, click Add permissions next to “Send As.” Choose the user and save.
Add a user for Send on Behalf. To let a user send email on behalf of the mailbox (the “on behalf of” note appears in the recipient’s email), use the “Send on Behalf” option in the same permissions panel.
Verify the permission. After saving, the user should see the mailbox in their Outlook (desktop, web, or mobile) automatically. If not, they can manually add it (see Tips).

Common Mistakes

Choosing the wrong admin center. The old Office 365 admin center doesn’t have these mailbox permission options. Use the Exchange admin center.
Giving Full Access when only Send As is needed. Full access allows reading and managing all content; Send As only allows sending. Over-permissioning is a security risk.
Forgetting to save. After adding a user, you must click Save in the permissions panel. Closing the panel without saving discards changes.
Not waiting for propagation. Permissions can take up to a few hours to fully propagate across Microsoft 365, especially in large organizations.

Tips

Use groups for multiple users. Instead of adding each user individually, you can grant permissions to a mail-enabled security group. This makes management easier.
Add the mailbox manually in Outlook. If the mailbox doesn’t appear automatically, the user can add it: In Outlook, go to File > Account Settings > Account Settings, select their email, click Change, then More Settings > Advanced > Add under “Mailboxes.” Type the mailbox name.
Use PowerShell for bulk changes. If you need to grant permissions to many mailboxes, use the Exchange Online PowerShell module with Add-MailboxPermission and Add-RecipientPermission cmdlets.
Test with a small mailbox first. Before rolling out to a large team, test the permission with a single user to ensure it works as expected.

Troubleshooting

User doesn’t see the mailbox in Outlook. Ask them to sign out and back in to Outlook, or restart the application. If it still doesn’t appear, manually add it as described in Tips.
Permission doesn’t work after several hours. Check that you saved the change in the Exchange admin center. Also verify that the user account is active and licensed (if applicable). If using a group, ensure the user is a member of that group.
Send As permission is not working. Note that “Send As” is different from “Send on Behalf.” If you need the email to appear from the mailbox, use “Send As.” Also, the user must compose a new email and manually select the “From” address (see FAQ).
Error: “You don’t have permission to open this mailbox.” This usually means the permission hasn’t propagated yet or was not saved. Re-check the permission settings and wait.

Frequently Asked Questions

How long does it take for mailbox permissions to work?

Usually it’s immediate, but in some cases it can take up to a few hours. If it’s been more than 24 hours, check your settings.

Can I give someone permission to a shared mailbox?

Yes, the process is the same. Shared mailboxes appear under Recipients > Shared in the Exchange admin center, but you can also manage permissions from the Mailboxes list.

How do I remove a permission?

In the same “Manage mailbox permissions” panel, click the “X” next to the user’s name and save.

Does the user need a license to access another mailbox?

No, the user only needs a license if they are also using their own mailbox. Access to another mailbox does not require an additional license.

Why can’t I see the “Send As” option?

The “Send As” option is only available in the Exchange admin center, not the Microsoft 365 admin center. Also, ensure you are looking at the correct mailbox’s permissions panel.

How do I send an email from the shared mailbox?

In Outlook, create a new email, click the “From” button, and select the mailbox you have access to. If you don’t see it, click “Other Email Address” and type the mailbox address.

Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.