How to Convert an Office 365 Mailbox to a Shared Mailbox

Let’s say a user has retired or quit. You, as administrator, want to convert the mailbox to a shared mailbox to free up the license the mailbox was using but keep the departed user’s important communications available or his or her successor to view and to intercept any emails that should now be addressed to that successor.

First, here are some really important things to you need to know:

  • The user mailbox you’re converting needs an Office 365 license assigned to it before you convert it to a shared mailbox. Otherwise, you won’t see the option to convert the mailbox.  If you’ve removed the license, add it back so you can convert the mailbox. After converting the mailbox to a shared one, you can remove the license from the user’s account.
  • Shared mailboxes can have up to 50GB of data without a license assigned to them. To hold more data than that, you need a license assigned to it.  You may need to delete a bunch of large emails (say, ones with attachments) from the shared mailbox to shrink it down so you can remove the license.
  • Don’t delete the old user’s account. That’s required to anchor the shared mailbox.  If you’ve already deleted the user account, see Convert the mailbox of a deleted user.

A license is not required for a shared mailbox provided you do not enable In-place Archive. If you are converting a user mailbox with an In-place archive to a shared mailbox, you’ll need export the archive to a pst before converting the mailbox.

Note: It’s probably a good idea to export the mailbox to a .pst file before converting, just in case the conversion doesn’t “take” properly.

Here’s how you convert a mailbox to a shared mailbox:

  1. Sign in with your Office 365 admin account at
  2. On the Active users page, select the user whose mailbox you want to convert.
  3. On the user’s page, expand Mail Settings and click Convert to shared mailbox. You won’t see this option if the user doesn’t have an Office 365 license assigned to them.
  4. Click Convert to complete the conversion. 
  5. If the mailbox is smaller than 50GB, you can remove the license from the user, and stop paying for it. Don’t delete the user’s old mailbox. The shared mailbox needs it there as an anchor. The user won’t be able to sign in using the old account.
  6. For everything else you need to know about shared mailboxes, please see Create a shared mailbox.

It will take a few minutes to convert the mailbox to shared. Once finished, if the mailbox is smaller than 50GB, remove the license from the mailbox in the Office 365 Admin center. Select the account, then click Edit next to the Assign license information on the right.


To Remove a License from Users in Office 365 Business

  1. In the Office 365 admin center, go to the Active users page, or choose Users > Active users.
  2. Select the box for the name of the user from whom you want to remove a license.
  3. On the right, in the Product licenses row, choose Edit.
  4. In the Product licenses pane, switch the toggle to the Off position for the license you want to remove from the user.
  5. At the bottom of the Product licenses pane, choose Save > Close > Close.  

Source 1: Diane Poremsky

Source 2: Diane Faigel

Source 2: