Last reviewed on December 12, 2014   —  20 Comments

After a user quit, an administrator wanted to convert the mailbox to a shared mailbox, to free up the license the mailbox was using. Because the user handled important communications, he didn’t want to delete the mailbox right away.

While I’d export the mailbox to a pst for backup, delete it and add the user’s address(es) to the mailbox of the person who took over the job, it is possible to convert a mailbox to a shared mailbox.

As of October 2014, the limits on shared mailboxes in the Small Business and Enterprise plans was raised to 50 GB. Shared mailboxes in Exchange Online Plan 1 and Plan 2 have a quota of 10 GB.

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.

Set-Mailbox -Type shared

If you are creating a shared mailbox in an Exchange Online Plan 1 or Plan 2, set the quota to 10GB before setting the mailbox to shared.

Set-Mailbox -Type shared -ProhibitSendReceiveQuota 10GB -ProhibitSendQuota 9.5GB -IssueWarningQuota 9GB
Set-Mailbox -Type shared

The Type parameter supports Regular, Room, Equipment, and Shared as values.

Verify the mailbox is now a shared mailbox:

Get-Mailbox -Identity | Format-List RecipientTypeDetails

use PowerShell to convert a mailbox type

After converting the mailbox, give other users Full Access and Send As permission as needed. You can do this from the Exchange Control Panel or using PowerShell.

To use PowerShell to give a user or group FullAccess rights:

Add-MailboxPermission username -User newuser -AccessRights FullAccess

To use PowerShell to give a user or group SendAs rights:

Add-RecipientPermission username -Trustee newuser -AccessRights SendAs

Assign fullaccess and send as permissions to the shared mailbox

Now you can remove the license from the account in Users and Groups. Two dialogs will warn you that removing the license will delete the mailbox and the contents, however, because you converted the mailbox to a shared mailbox before removing the license, the mailbox won't be deleted. Note: while the mailbox contents are safe, Lync contacts may be lost.

The first dialog:
Are you sure you want to delete the license

The second dialog reads:

Are you sure you want to remove the Exchange license?

The user’s mailbox and all messages in it are deleted. We recommend that you only delete licenses from users who no longer need email.
All email aliases associated with the user account are deleted. If you need someone in your company to receive email at those aliases, assign them to another user.
Their Lync Contacts list may be deleted. To restore their Lync Contacts, assign the user an Exchange license within 30 days. If you want to remove their Exchange license but keep their Lync Contacts, contact Support before you remove the Exchange license.

More Information

More information is available at Convert a Mailbox (TechNet)


  1. Mike says

    great article!!! especially for a novice like me. i do have to say though i am lost at the last part where you say

    "Now you can remove the license from the account in Users and Groups."

    where is that done? i can't find it

  2. Avinash Illindra says

    Thanks for the great article, it will be very helpful article.

    I have a small doubt on Second dialog:

    We lost the mails surely or is there any alteration for without loosing mails.

    Avinash Illindra

    • Diane Poremsky says

      Unless the mailbox is over 5 GB or is using an online archive, you won't lose any messages. If there is more than 5 GB in the mailbox, the mailbox may be truncated - if you are using an online archive, it will be lost. The mailbox should be recoverable though.

  3. says

    I'm looking to convert a regular mailbox to a shared mailbox and was looking at risks in doing so. I wanted to confirm your 5gb limit for shared mailboxes, but the technet site says 50gb for shared mailboxes on 365 Enterprise. Can you confirm?

    • Diane Poremsky says

      They recently raised the shared quota for a *free* license to 10 GB. You can create a shared mailbox with a higher quota but will need to assign a license to it.

      Looks like they changed the quota again - it's now 50GB, no license required unless you need online archiving.

    • Diane Poremsky says

      which command does it say is the problem? I noticed today that there was a space after one dash - there is not supposed to be a space between the dash and the parameters.

  4. Andy says

    Like this Idea. Thanks! However I'd like to rename the mailbox to indicate it is for a former employee, my problem is that the object is synced with AD. I can rename it in AD but at some point the AD object will be deleted and the mailbox won't be. Is there a way to break AD sync for one object.
    If not, it's a question of exporting from a user mail box them importing to a shared one. A bit time consuming to say the least. lol.

    • Diane Poremsky says

      AFAIK, there is no way to break the sync with the AD - you need to keep the unlicensed user. You might be able to rename it, but it will still be linked to the AD object.

  5. Charlie says

    That didn't seem to work for me. i converted to Shared, deleted the user, and then it delete the Shared inbox also. Lucky I still took a backup.

  6. Matthew Marlowe says

    This didn't work for me. I converted to Shared, then just removed the license and it deleted the Exchange box. It's gone. ;(

    • Diane Poremsky says

      That's not supposed to happen if you convert to shared before removing the license. Are you using Office 365 or an on premise exchange server?

      It should be recoverable for up to 24 hours, if not longer.

  7. Bob says

    For online archive, you need to backup the online archive to a .pst file, create a shared mailbox, export the .pst file to the shared mailbox and you then have the mailarchive of the old user.
    My question is though, if we delete the user first (after backing up the email to .pst), and then create a shared mailbox with that uses name, would emails still arrive in the inbox just as if the user is still active?
    As I alrady have other shared mailboxes setup that are receiving emails from external users, I am assuming this would be the case?

    • Diane PoremskyDiane Poremsky says

      The messages would arrive in the shared mailbox if the smtp address was the same as before. you can export the mail to a pst then remove the online archive and switch it to shared. That might be easier than deleting and recreating.

  8. JD in MN says

    I didn't understand that we need to keep shared mailboxes as a user, but not need a license. Delete the license--don't delete from active users.

    I was able to remove the license in Exchange Online Admin, after converting to shared mailbox, without using Powershell.

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