How to Convert a User Mailbox to a Shared Mailbox

To convert a mailbox to shared in Microsoft 365 (Office 365), the user needs a license assigned when you convert. You remove it afterwards if the mailbox is under 50 GB. If the license is already gone, add it back first, or the convert option does not appear.

On this page: the quick steps, converting without a license, PowerShell, blocking sign-in, the 50 GB limit, archive and holds, and converting back. The steps follow Microsoft Learn's Convert a user mailbox to a shared mailbox, checked in November 2026.

1. 1

   Keep the license on the user

   Do not remove the license before converting. Without one, the Convert to shared mailbox option does not appear. If it was already removed, reassign it, convert, then remove it again.

2. 2

   Open the user in the admin center

   In the Microsoft 365 admin center go to Users > Active users and select the user.

3. 3

   Convert the mailbox

   On the Mail tab select Convert to shared mailbox, then select Convert. All existing email and calendar data is retained.

4. 4

   Check the size, then remove the license

   If the mailbox is under 50 GB, remove the license from the user and stop paying for it. Do not delete the user account: the shared mailbox needs it as an anchor.

5. 5

   Block sign-in on the converted account

   Unless you reset the password, the original username and password keep working on the shared mailbox. Go to Users > Active users, select the user, select Block sign-in, choose Block this user from signing in, and save.

6. 6

   Grant access

   Add members under Teams & groups > Shared mailboxes. Full Access lets a member read the mailbox. Send As makes replies come from the shared address. Assign both if people need to read and reply.

7. 7

   Verify the result

   In Exchange Online PowerShell, Get-Mailbox -Identity [email protected] | Select RecipientTypeDetails should return SharedMailbox.

Can you convert a user to a shared mailbox without a license?#

No, not directly. Microsoft states that the user mailbox needs a license assigned before you convert it, otherwise you will not see the option. The same page then says that after converting you can remove the license from the user's account.

So the working order for an unlicensed user is: assign a license, convert, then remove the license if the mailbox is under 50 GB. If the account was already deleted, restore it first (see the section on deleted users below).

Do you need a license after the conversion?#

Usually not. Shared mailboxes are limited to 50 GB without a license. Microsoft says you might need to delete large messages to shrink the mailbox so you can remove the license. For the full rules see does a shared mailbox need a license.

PowerShell: convert to shared mailbox in Exchange Online#

PowerShell is the better path when you convert several mailboxes or want a scripted, repeatable offboarding step. Connect to Exchange Online PowerShell, convert, then check the type. The license still has to be on the mailbox when you run it, and you remove it afterwards in the admin center.

For several mailboxes, put the addresses in a CSV file with an Address column and loop over it. Run it on one test mailbox first.

Block sign-in on the converted account#

Microsoft's note is easy to miss: if you do not reset the password, the original username and password continue to work on the shared mailbox after conversion. A shared mailbox account is not meant to be signed in to directly, and for a leaver you want those credentials dead.

Block sign-in in the admin center (Users > Active users > the user > Block sign-in). Microsoft notes blocking can take up to 24 hours to take effect, and that resetting the password is what cuts access immediately. For a departing employee, Microsoft's Remove a former employee series covers the full list, including signing out of all sessions.

What happens to rules, archive and holds#

Inbox rules are preserved after the conversion, according to Microsoft. Calendar and email data are retained too. The old user's automatic reply is worth a manual check, so a departed employee's out-of-office does not keep greeting senders.

Archives and holds are where a license matters. Microsoft says a shared mailbox needs Exchange Online Plan 2, or Plan 1 plus the Exchange Online Archiving add-on, to put a litigation hold or In-Place Hold on it, and to enable auto-expanding archiving. Microsoft does not spell out what happens to an existing archive when you remove a license, so check the hold and archive status first and keep a qualifying license until legal has decided.

Which method should you use?#

Use the Microsoft 365 admin center for a single mailbox, where you can see each step. Use Exchange Online PowerShell for several mailboxes or an auditable script. Both produce the same shared mailbox, and the license is removed in the admin center either way.

What to do when the conversion does not work#

Symptom, cause and fix:

• Convert to shared mailbox is missing: the license was removed. Assign a license, wait for the mailbox to sync, then convert again. If the license is present, confirm your admin account can manage users and mailboxes
• Still a user mailbox after a while: check RecipientTypeDetails in PowerShell. If it returns UserMailbox, run Set-Mailbox -Type Shared and read any error output. Room and equipment mailboxes are a different type and are not covered by this guide
• Mailbox over 50 GB after removing the license: trim it, or assign Exchange Online Plan 2 to raise the limit to 100 GB. Microsoft says a full shared mailbox stops sending first and later stops receiving
• Members cannot see the shared mailbox in Outlook: see shared mailbox not showing in Outlook, which covers automapping delays and permissions

How to convert a shared mailbox back to a user mailbox#

You can reverse it. Microsoft's steps: open the Exchange admin center, go to Recipients > Mailboxes, select the shared mailbox, and on the Others tab select Convert to regular mailbox and confirm. Then, in the Microsoft 365 admin center, assign a license to the associated user account and reset the password.

It takes a few minutes for the mailbox to be set up. When the person signs in, they see the email and calendar items that used to be in the shared mailbox. PowerShell with Set-Mailbox -Type Regular is the scripted alternative.

What if the user account was already deleted?#

The shared mailbox needs the old user account as its anchor, so do not delete it. If it is already deleted, Microsoft's steps are: restore the user's account, make sure a license is assigned, reset the password, and allow up to 24 hours for the mailbox to be re-created. Then remove the license, keep the account, and add members.

Microsoft's offboarding guidance also says a deleted account's email and OneDrive content is retained for 30 days, during which you can restore the account. For the wider process see what to do with a mailbox when an employee leaves. For the permission choices after conversion, read Full Access vs Send As vs Send on Behalf.

Where AI Emaily fits#

Converting a mailbox is a Microsoft admin job, and AI Emaily does not do it. AI Emaily connects the Outlook or Microsoft 365 mailbox you sign in with and cannot open Microsoft shared mailboxes. If your own inbox needs help, there is a 7-day free trial on Pro or Autopilot. We build AI Emaily.