Convert a user mailbox to a shared mailbox

What you need before step 1

Applies to: Exchange Online mailboxes in Microsoft 365, including cloud-provisioned mailboxes in an Exchange hybrid organisation, as documented by Microsoft

9 steps

1. 1

   Check the mailbox type and size

   Where: PowerShell on your admin PC, connected with Connect-ExchangeOnline

   Connect (see connect to Exchange Online PowerShell), then confirm it is a user mailbox and check its size. If TotalItemSize is over 50 GB, either keep an Exchange Online Plan 2 licence on it after conversion or delete large items first.

   Connect-ExchangeOnline -UserPrincipalName admin@contoso.com
   Get-Mailbox -Identity user@contoso.com | Format-List DisplayName,RecipientTypeDetails,LitigationHoldEnabled
   Get-EXOMailboxStatistics -Identity user@contoso.com | Format-List DisplayName,TotalItemSize,ItemCount

   You should see: RecipientTypeDetails shows UserMailbox, and TotalItemSize shows the current size, for example 12.3 GB.
2. 2

   Make sure the licence is still assigned

   Where: Microsoft 365 admin center (https://admin.microsoft.com) > Users > Active users > (user) > Licenses and apps

   Check a licence that includes Exchange Online is ticked. If you removed it already, tick it again and select Save changes; Microsoft says you will not see the convert option otherwise. See assign licences in Microsoft 365.

   You should see: The Licenses and apps tab shows a licence with Exchange Online.
3. 3

   Convert in the Microsoft 365 admin center

   Where: Microsoft 365 admin center > Users > Active users

   Select the user. On the Mail tab, select Convert to shared mailbox, then select Convert. Use this, the EAC (next step) or PowerShell (step 5); you only need one.

   You should see: A confirmation that the mailbox was converted. The user now appears in Teams & groups > Shared mailboxes.
4. 4

   Or convert in the Exchange admin center

   Where: Exchange admin center (https://admin.exchange.microsoft.com) > Recipients > Mailboxes

   Select the mailbox. In the More actions pane select Convert to shared mailbox, then select Confirm.

   You should see: The notification Mailbox converted successfully is displayed, and the mailbox type shows Shared.
5. 5

   Or convert with PowerShell

   Where: PowerShell connected with Connect-ExchangeOnline

   Run Set-Mailbox with -Type Shared. For several mailboxes, put the addresses in a CSV with a header Email and loop through it.

   Set-Mailbox -Identity user@contoso.com -Type Shared
   Import-Csv C:\migration\to-shared.csv | ForEach-Object { Set-Mailbox -Identity $_.Email -Type Shared }

   You should see: The prompt returns with no error.
6. 6

   Hybrid only: convert the remote mailbox on-premises

   Where: Exchange Management Shell on an on-premises Exchange server

   If directory synchronisation manages the account, Microsoft says to manage the mailbox with on-premises tools. For a mailbox provisioned in Exchange Online but not migrated, convert the remote mailbox object on-premises. If the mailbox was migrated to Exchange Online, also update the mailbox in Exchange Online (step 5). Otherwise the next sync can turn it back into a user mailbox.

   Set-RemoteMailbox -Identity user@contoso.com -Type Shared

   You should see: The command completes with no error, and after the next sync Exchange Online still shows the mailbox as Shared.
7. 7

   Give people access

   Where: Microsoft 365 admin center > Teams & groups > Shared mailboxes, or PowerShell connected with Connect-ExchangeOnline

   Select the shared mailbox and edit its Members to add the people who need it, or grant Full Access and Send As in PowerShell. Microsoft says a shared mailbox supports a maximum of 25 users at once; use a Microsoft 365 group if you need more. Only people inside your organisation can use a shared mailbox.

   Add-MailboxPermission -Identity user@contoso.com -User colleague@contoso.com -AccessRights FullAccess -InheritanceType All
   Add-RecipientPermission -Identity user@contoso.com -Trustee colleague@contoso.com -AccessRights SendAs -Confirm:$false

   You should see: The colleague is listed as a member, and the shared mailbox appears in their Outlook folder list after Outlook restarts.
8. 8

   Block sign-in to the old account

   Where: Microsoft 365 admin center > Users > Active users > (user)

   Select Block sign-in, tick Block this user from signing in and select Save changes. Microsoft says the original username and password keep working on a converted shared mailbox unless you change them, and that you should always block sign-in for shared mailbox accounts.

   You should see: The user shows Sign-in blocked in Active users. Members can still open the mailbox through their own accounts.
9. 9

   Remove the licence if the mailbox is under 50 GB

   Where: Microsoft 365 admin center > Users > Active users > (user) > Licenses and apps

   Untick the licence and select Save changes. Keep a licence if the mailbox is over 50 GB, has an archive you need beyond the default, or must stay on Litigation Hold or In-Place Hold (Exchange Online Plan 2, or Plan 1 plus Exchange Online Archiving).

   You should see: The user shows Unlicensed and the shared mailbox still opens for members.

Expert tips

How to confirm it worked

• Get-Mailbox -Identity user@contoso.com | Format-List RecipientTypeDetails returns SharedMailbox.

• Microsoft 365 admin center > Teams & groups > Shared mailboxes lists the mailbox with its members.

• A member opens the mailbox in Outlook on the web (select their profile picture > Open another mailbox) and sees the old mail, calendar and inbox rules (Microsoft says inbox rules are preserved).

• Signing in directly as the old user fails because sign-in is blocked.

How to reverse it

Errors you might see

Questions

Official sources

Vendors change menus and requirements. Confirm on the source before you rely on a detail. Last checked 4 Nov 2026.