How to Create and Manage a Shared Mailbox in Microsoft 365

A shared mailbox gives a team a common address for customer service, reception, sales, or general enquiries. Members can read incoming messages and send replies from the shared address instead of using personal mailboxes.

Understand when to use a shared mailbox

Shared mailboxes are designed for multiple people who need access to the same inbox and calendar. Common examples include support, reception, and company information addresses. Microsoft says users with the appropriate permissions can send as or send on behalf of the shared mailbox. [1]

A shared mailbox is not intended for direct sign-in. Keep the associated account blocked and grant access through each user’s own licensed Exchange Online mailbox. [1]

1. Open the shared mailboxes page

1. Sign in to the Microsoft 365 admin center with an Exchange administrator role.
2. Open Teams & Groups > Shared mailboxes.
3. Select Show all in the left navigation if the section is not visible.

If you do not have the required role, Microsoft will display a permission error. Ask an administrator to create the mailbox or assign the appropriate administrative role.

2. Create the mailbox

1. Select + Add a shared mailbox.
2. Enter a display name, such as Customer Support.
3. Review the proposed email address and edit it if needed.
4. Select Save changes.
5. Wait a few minutes, then select Add members to this mailbox.

Creating the mailbox also creates a shared calendar. Members can use it for appointments that the team needs to see and manage. [2]

3. Add the mailbox members

1. Select Add members.
2. Choose the users who should read incoming messages and use the shared mailbox.
3. Select Add, then close the member picker.

Only users inside your organization can use a shared mailbox. Each person should use their own identity so access can be reviewed and removed when their role changes. [1]

4. Choose the right permissions

Microsoft documents three common permission types:

• Full Access: lets a user open the mailbox and read, create, modify, and delete messages, calendar items, contacts, and tasks.
• Send As: makes the outgoing message appear to come from the shared mailbox.
• Send on Behalf: shows that an individual sent the message on behalf of the shared mailbox.

Full Access alone does not allow a user to send from the shared address. For normal shared-mailbox operation, grant Full Access plus Send As, or use Send on Behalf when that wording is important. [2]

5. Edit delegation in Exchange admin center

1. Open the Exchange admin center.
2. Go to Recipients > Mailboxes.
3. Select the shared mailbox and choose Edit.
4. Under Mailbox permissions, select Manage mailbox delegation.
5. Add or remove users for Full Access and Send As.
6. Select Save.

Review the member list and delegation list together. Removing a member but leaving separate delegation in place can create unexpected access.

6. Open the mailbox in Outlook

When automapping is enabled, the shared mailbox normally appears in Outlook after the user closes and restarts the app. Automapping is assigned through the user’s mailbox permissions, so managing access only through a security group may not produce the expected automatic mapping. [2]

7. Check licensing and limits

Microsoft says an unlicensed shared mailbox can store up to 50 GB. An Exchange Online Plan 2 license is required for scenarios such as more than 50 GB, in-place archiving, or litigation hold. Users accessing the mailbox still need their own licensed Exchange Online mailbox. [1]

A shared mailbox also has operational limits. Microsoft notes that too many simultaneous users can cause connection failures or duplicated messages, and recommends a Microsoft 365 group when more than 25 users need access.

Common mistakes

• Granting Full Access but forgetting Send As or Send on Behalf.
• Allowing direct sign-in to the shared mailbox account.
• Assuming an unlicensed mailbox can exceed 50 GB indefinitely.
• Leaving former staff in the member or delegation list.
• Using a shared mailbox when the team needs stronger deletion controls or a larger collaboration group.

Sources

1. Microsoft Learn: About shared mailboxes in Microsoft 365
2. Microsoft Learn: Create a shared mailbox
3. Microsoft Learn: Create shared mailboxes in the Exchange admin center