Shared Mailbox in Microsoft 365: Licensing, Permissions and Best Practices

Shared Mailbox in Microsoft 365: Licensing, Permissions and Best Practices

Originally published 10 October 2020 · Reviewed 5 November 2026

A shared mailbox lets a team receive and send email from a common address such as support@ or accounts@, without sharing a password and without giving each member another mailbox. It is one of the most useful and most misused parts of Exchange Online. This guide covers what it is, how permissions and licensing work, and how to keep it secure. Details change with Microsoft 365 updates, so confirm the current rules on Microsoft's pages before you rely on a limit.

What a shared mailbox is

A shared mailbox is a mailbox that has no direct user of its own. People reach it because an administrator grants them permissions, and it appears in their Outlook and Outlook on the web beside their own mailbox. It has an inbox, a calendar, contacts and folders like any mailbox. Because nobody logs in as the shared mailbox, there is no separate password to share, and each person's actions can be traced to their own identity.

An older article may say that shared mailboxes are not supported on mobile devices. That is out of date: current Outlook mobile apps can open shared mailboxes that you have access to. Check Microsoft's Outlook mobile documentation for the current behaviour on your platform.

Permissions

There are three distinct permissions, and mixing them up causes most support tickets:

• Full Access. The user can open the mailbox and read and manage its contents. With auto-mapping, the mailbox may appear automatically in the user's Outlook.
• Send As. The user can send a message that appears to come from the shared address, with no sign that another person sent it.
• Send on Behalf. The user can send a message that shows as sent by the user "on behalf of" the shared mailbox.

A user can have any combination. A team inbox usually needs Full Access and Send As. Grant the minimum. Replies sent from the shared address by a user with Send As appear to come from the shared mailbox.

By default, messages sent from a shared mailbox are saved in the sender's Sent Items, not the shared mailbox's. Administrators can change the setting so that a copy is also stored in the shared mailbox, which makes conversations easier to follow for the whole team.

Licensing

Microsoft states that a shared mailbox does not need a licence if it is smaller than 50 GB and you do not need extra features. A licence is needed when you want a mailbox larger than 50 GB, or features such as an online archive or litigation hold. The relevant licence is typically Exchange Online Plan 2, though available plans change, so check the current Microsoft 365 service description. The people who access the mailbox need their own licensed mailboxes; a shared mailbox is not a substitute for a user licence.

How to create and manage one

In the Microsoft 365 admin center, you create a shared mailbox under Teams and groups, choose a name and email address, then add members. In the Exchange admin center or PowerShell, you can set the permissions listed above individually and adjust sent items behaviour. Use consistent names and document who owns each shared mailbox.

Security best practices

• Block sign-in for the shared mailbox account. It should be accessed only through users with permissions. If it can be signed in to directly, someone may set a password, and it will bypass your multifactor authentication and Conditional Access controls.
• Use least privilege. Do not give the whole company Full Access to a mailbox that holds sensitive messages.
• Review access regularly. Many shared mailboxes outlive the project that created them. Access reviews, or a quarterly check of permissions, remove unneeded access.
• Watch for forwarding rules and delegations. Attackers use mailbox rules to hide or redirect mail; inspect them for shared mailboxes too.
• Audit sends. Send As actions can be searched in audit logs, which helps if a message is disputed.
• Do not use a shared mailbox as a general login. For automated sending, use the connector or application options that suit the task, not a shared mailbox password.

Alternatives

If you need a shared inbox with ownership, comments and assignment, consider whether Microsoft 365 Groups or a ticketing system fit better. A distribution list is only a forwarding address, not a place to keep mail. A shared mailbox is best when a few people must read and answer one address and need the history in one place.

Common problems

• The mailbox does not appear in Outlook. Permissions can take time to propagate, and auto-mapping may be disabled. Add the mailbox manually.
• Messages from the shared address show the wrong sender. Check whether the user has Send As or Send on Behalf, and which address is selected in the From field.
• Replies are not in the shared Sent Items. Enable copying sent items for the shared mailbox.
• The mailbox is full. Review retention and archive options, and licence it if you need more space or features.
• A former employee still has access. Include shared mailboxes in your leaver checklist.

Microsoft references

• About shared mailboxes, reviewed 5 November 2026.
• Create a shared mailbox, reviewed 5 November 2026.

This article was first published on 10 October 2020. It was rewritten on 5 November 2026 to correct outdated statements such as mobile support. Microsoft's live documentation takes precedence if it has changed.