Overview

A shared mailbox in Exchange Online allows multiple users to read and send email from a common address such as info@contoso.com or support@contoso.com. Shared mailboxes do not require a license unless the mailbox exceeds 50 GB or uses archive features.
Microsoft recommends creating shared mailboxes via the Microsoft 365 admin center, which automatically handles permissions and membership assignment.

Step 1 — Create the Shared Mailbox (Microsoft 365 Admin Center)

(From Microsoft doc: Create a shared mailbox)

1. Go to https://admin.microsoft.com.

2. Navigate to Teams & groups → Active teams & groups.

3. Select Add a group.

4. Choose Shared mailbox as the group type.

5. Enter Name and Email address.

6. Add Members who should have access.

7. Click Create.

Microsoft 365 automatically assigns Full Access and Send As permissions to all added members.

Step 2 — Assign Users or Groups as Members

Option 1 — Add Individual Users

1. In the Admin Center, open the shared mailbox.

2. Select Members → Edit.

3. Add or remove individual users.

4. Save.

Option 2 — Add a Group (Recommended for larger teams)

Shared mailboxes support group-based access management, which simplifies permissions for large teams or rotating staff.

Requirements:
✔ The group must be a mail-enabled security group.
❌ Microsoft 365 Groups are NOT supported for shared mailbox permissions.
❌ Security groups without mail capability are NOT supported.

How to assign a group:

1. Create or verify a mail-enabled security group in the Microsoft 365 admin center or Exchange admin center.

2. Add required users to that group.

3. Assign the group to the shared mailbox under:
   Microsoft 365 admin center → Shared mailbox → Members → Add group

4. The group will receive Full Access + Send As permissions.

Best practice: Always use mail-enabled security groups for dynamic membership (Teams changing, large helpdesk groups, NOC teams, etc.)

Step 3 — Optional: Configure Permissions in Exchange Admin Center

(For advanced or manual control)

1. Go to https://admin.exchange.microsoft.com.

2. Navigate to Recipients → Shared.

3. Select the shared mailbox → Mailbox Delegation.

4. Configure:

   • Full Access

   • Send As

   • Send on Behalf

Group assignment here also requires a mail-enabled security group.

Step 4 — How Users Access the Shared Mailbox

Outlook Desktop

• Auto-maps to Outlook if Full Access is applied.

• If not visible, restart Outlook.

Outlook on the Web (OWA)

1. Click profile photo → Open another mailbox.

2. Enter mailbox address.

Outlook Mobile

• Add shared mailbox as secondary account
  OR

• Use the Outlook Mobile “Shared Mailbox” option.

Licensing Requirements

✔ No license needed for shared mailbox ≤ 50 GB
✔ License required if:

• Mailbox > 50 GB

• Archive mailbox needed

• Auto-expanding archive enabled

• Direct login required

Troubleshooting

Shared mailbox not in Outlook

• Wait up to 60 minutes

• Restart Outlook

• Reassign Full Access (auto-mapping may be delayed)

Send As not working

• Replication time: Up to 2 hours

• Re-add permissions if needed

Group not applying permissions

• Ensure the group is mail-enabled security group

• Ensure the group is replicated in Exchange Online

Create a shared mailbox - Microsoft 365 admin | Microsoft Learn

Shared mailboxes in Exchange Online | Microsoft Learn