Convert a user mailbox to a shared mailbox

Shared Mailboxes & Mailbox Permissions in Microsoft 365

A shared mailbox is an email inbox that multiple people can read and send from, without each person needing a separate paid licence. They are ideal for team inboxes such as support@yourdomain.co.uk, sales@yourdomain.co.uk, or info@yourdomain.co.uk.

This guide covers creating shared mailboxes, granting access, setting send permissions, and converting existing mailboxes.

Creating a New Shared Mailbox

1. Sign in to admin.microsoft.com.
2. Go to Teams & groups → Shared mailboxes.
3. Click Add a shared mailbox.
4. Enter a Name (the display name, e.g. "Support Team") and an Email address (e.g. support@yourdomain.co.uk).
5. Click Save changes.
6. The mailbox is created. Now add members who need access.

Adding Members to a Shared Mailbox

1. From the Shared mailboxes list, click on the mailbox you just created.
2. Under Members, click Edit.
3. Click Add members, search for each user and click Add.
4. Click Save.

Members will need to add the shared mailbox to their Outlook profile before it appears (see below).

Accessing a Shared Mailbox in Outlook

Outlook desktop (Windows / Mac)

1. Outlook will usually add the shared mailbox automatically within 30 minutes of being granted access.
2. If it does not appear, go to File → Account Settings → Account Settings.
3. Click on your Microsoft 365 account → Change → More Settings → Advanced.
4. Under Open these additional mailboxes, click Add and enter the shared mailbox address.
5. Click OK → Next → Done. The mailbox will appear in the left panel.

Outlook on the web (OWA)

1. Sign in at outlook.office.com with your own account.
2. Right-click Folders in the left panel.
3. Click Add shared folder or mailbox.
4. Type the shared mailbox address and click Add.

Sending Email from a Shared Mailbox

Members with Send As permission send email that appears to come from the shared mailbox address — recipients see the shared address, not the individual's name.

Members with Send on Behalf permission send email that shows both the sender and the mailbox (e.g. "Jane Smith on behalf of Support Team").

Granting Send As permission

1. Go to Teams & groups → Shared mailboxes and click the mailbox.
2. Under Send As permissions, click Edit.
3. Click Add permissions, select the user(s) and click Add.
4. Click Save.
5. Note: Permission changes can take up to 60 minutes to take effect.

Sending from the shared mailbox in Outlook

1. Click New email.
2. Click From (if you cannot see this field, click Options → From).
3. Select the shared mailbox address from the dropdown, or click Other email address and type it.
4. Compose and send as normal.

Converting a User Mailbox to a Shared Mailbox

This is useful when an employee leaves and you want to retain their email history as a shared inbox.

1. Go to Teams & groups → Shared mailboxes.
2. Click Convert to shared mailbox (or go to Users → Active users, click the user, and look for the Mail tab → Convert to shared mailbox).
3. Enter the user's email address and click Convert.
4. Once converted, remove the user's licence — shared mailboxes do not require a paid licence (up to 50 GB).
5. Add team members who need access to the converted mailbox.

Important: Shared mailboxes larger than 50 GB require an Exchange Online Plan 2 licence or Microsoft 365 licence with that plan.

Mailbox Delegation (Full Access)

Full Access permission lets a user open another person's mailbox and manage it, but does not allow them to send email as that person (use Send As for that).

Grant Full Access to a user's mailbox

1. Go to Users → Active users and click on the mailbox owner's account.
2. Click the Mail tab.
3. Under Mailbox permissions, click Read and manage email (Full Access) and click Edit.
4. Click Add permissions, select the delegate user, and click Add.
5. Click Save changes.

Setting Up an Auto-Reply on a Shared Mailbox

1. Sign in to outlook.office.com with your own account.
2. Open the shared mailbox (via the folder panel on the left).
3. Click the settings cog ( ⚙ ) in the top right.
4. Search for Automatic replies and click it.
5. Toggle Automatic replies on.
6. Enter your reply message and set the date range if required.
7. Click Save.

Troubleshooting

Shared mailbox not appearing in Outlook

• Confirm the user has been added as a member in the admin centre. Permission changes can take up to 1 hour to appear.
• Restart Outlook. If still missing, manually add the mailbox via File → Account Settings (see instructions above).
• On Outlook web, use Add shared folder or mailbox from the folder panel.

Cannot send from the shared mailbox address

• Verify the user has Send As permission, not just Full Access.
• Wait 60 minutes after granting Send As permission before testing.
• In Outlook, ensure the From field is visible and the correct address is selected.

Shared mailbox is over the 50 GB limit

• Assign an Exchange Online Plan 2 or Microsoft 365 licence to the shared mailbox to raise the limit to 100 GB and enable archiving.

Converting a mailbox fails

• Ensure the user's mailbox is not in a litigation hold or compliance retention policy — these prevent conversion.
• Contact support if the option to convert is greyed out.

Related Guides

• Basic mailbox settings for Outlook and other email clients (POP/IMAP)
• Diagnostics log collection in Support and Recovery Assistant
• Add an Outlook.com or Office 365 account
• How to Create Email Account in the Control Panel
• Groups naming policy

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