Convert a user mailbox to a shared mailbox

When you convert a user's mailbox to a shared mailbox, all of the existing email and calendar is retained. Only now it's in a shared mailbox where several people will be able to access it instead of one person. At a later date, you can convert a shared mailbox back to a user (private) mailbox.

Here are some really important things that you need to know:

• The user mailbox you're converting needs a 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 50 GB 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.

• The rules are intact after the mailbox is converted to a shared mailbox.

Use the Exchange admin center to convert a mailbox

1. Go to the Exchange admin center.

2. Select Recipients > Mailboxes.

3. Select the user mailbox. Under Convert to Shared Mailbox, select Convert.

4. If the mailbox is smaller than 50 GB, you can remove the license from the user, and stop paying for it. Don't delete the user's account. The shared mailbox needs it there as an anchor. If you are converting the mailbox of an employee that is leaving your organization, you should take additional steps to make sure that they cannot log in anymore. Please see Remove a former employee from Microsoft 365.

For everything else you need to know about shared mailboxes, see About shared mailboxes and Create a shared mailbox.

Convert the mailbox of a deleted user

Let's say you've deleted a user account and now you want to convert their old mailbox to a share mailbox. Here's what you need to do:

1. Restore the user's account.

2. Make sure a Microsoft 365 license is assigned to it.

3. Reset the user's password.

4. Wait 20-30 minutes for their mailbox to be recreated.

5. Now follow the instructions on this page to convert their mailbox to a shared mailbox.

6. After that's done, you can remove the license from the user's mailbox. Don't delete the user's old mailbox. The shared mailbox needs it there as an anchor.

7. Add members to the shared mailbox.

Convert a shared mailbox back to a user's (private) mailbox

1. Go to the Exchange admin center.

2. Select Recipients > Shared.

3. Select the shared mailbox. Under Convert to Regular Mailbox, select Convert.

4. Go back to the admin center. Under Users, choose the user account associated with the old shared mailbox. Assign a license to the account, and reset the password.

   It will take a few minutes for the mailbox to get set up, but after that, the person who is going to use that account is ready to go. When they sign in, they'll see the email and calendar items that used to be in the shared mailbox.

Convert a user's mailbox in a hybrid environment

For more info about converting a user mailbox to a shared mailbox in an Exchange Hybrid environment, see:

• Cmdlets to create or modify a remote shared mailbox in an on-premises Exchange environment
• Shared mailboxes are unexpectedly converted to user mailboxes after directory synchronization runs in an Exchange hybrid deployment