Multiple users can access a shared mailbox in Exchange. Unlike a common user mailbox, a shared mailbox account is disabled in Active Directory and cannot be used for interactive sign-in. This article describes how to convert a common user mailbox to a shared mailbox in on-premises Exchange Server and Microsoft 365.

When you convert a user mailbox to a shared mailbox, only the mailbox type is changed. All existing e-mail messages and calendar items, mailbox and folder permissions, as well as mailbox rules, are retained.

You may need to convert a user mailbox to a shared one when:

• If you want to share a mailbox with multiple users, use a shared calendar when scheduling;
• The user leaves the organization and you want to share the mailbox contents with the remaining employees;
• No separate license is required for a shared mailbox

How to Convert a User Mailbox to a Shared on Exchange Server with PowerShell?

In the on-premises Exchange Server 2019/2016/2013, you can convert a user mailbox to a shared mailbox using Set-Mailbox PowerShell cmdlet. Use the syntax below:

Set-Mailbox -Identity <MailboxIdentity> -Type <Regular | Room | Equipment | Shared>

Open the PowerShell console and connect to your Exchange Server. Check the mailbox type with the command:

Get-Mailbox -Identity a.shepherd| Format-Table Name, RecipientTypeDetails

This is a common user mailbox (UserMailbox).

In order to convert it to a shared mailbox, run the following command:

Set-Mailbox a.shepherd -Type Shared

The mailbox type has changed to SharedMailbox.

To convert multiple user mailboxes to shared mailboxes at once, create a CSV file with a list of users (remember to add the Email line to the first line of the file). Then import the CSV file and change the mailbox type:

Import-CSV C:\Reports\EXCH\user_to_shared_mailbox.csv | foreach {Get-Mailbox -Identity $_.Email | Where-Object {$_.RecipientTypeDetails -eq "UserMailbox"} | Set-Mailbox -Type Shared}

If you want to convert a shared mailbox back to a user one, run this command:

Set-Mailbox a.shepherd -Type Regular

Converting a User Mailbox to a Shared Mailbox in Exchange Online (Microsoft 365)

In Exchange Online, you may convert a user mailbox to a shared one using the Exchange Admin Center (EAC) or PowerShell.

1. 1. Sign in to the Exchange Admin Center;
   2. Go to Recipients –> Mailboxes;
   3. Select a user whose mailbox you want to convert;
   4. Navigate to the Others tab and click Convert to shared mailbox;
   5. Confirm mailbox conversion;
   6. If the mailbox size is less than 50 GB, you may remove its Microsoft 365/AzureAD license.
      The size of a shared mailbox without a license may not exceed 50 GB. Check the current Exchange mailbox size and clear its contents if it is more than 50 GB.

Also, you can convert a user mailbox to a shared one using PowerShell. Connect to your Microsoft 365 tenant using the EXO PowerShell module:

Connect-ExchangeOnline

To change the mailbox type to SharedMailbox, run the command below:

Set-Mailbox –Identity?a.shepherd -Type Shared

You may convert it back in the same way:

Set-Mailbox –Identity?a.shepherd -Type Regular