Convert a User Mailbox to a Shared Mailbox in a Hybrid Environment

Converting a user mailbox to a shared mailbox in a hybrid Exchange environment can be frustrating. Converting a remote mailbox via the on-premise Exchange Admin Center is not an option and converting the mailbox in the Microsoft 365 Exchange Admin Center results in inconsistencies between the on-premise environment and Microsoft 365.

For years Microsoft's recommendation involved migrating the mailbox you want to convert to the on-premise Exchange environment, converting the mailbox, and migrating the converted mailbox back to Microsoft 365. This process is very time consuming, especially for large mailboxes.

Fortunately, there is a PowerShell command available that makes the entire process much simpler.

---

Instructions

• Convert Mailbox in Microsoft 365
• Update the On-Premise User

---

Convert Mailbox in Microsoft 365

1. Login to the Microsoft 365 Exchange Admin Center, click on Recipients, then choose the Mailboxes tab.

2. Select the mailbox that you want to convert and click the Convert link under the Convert to Shared Mailbox heading in the right pane.

   

3. Click Yes on the warning prompt to proceed with the conversion.

   

---

Update the On-Premise User

Open Exchange Management Shell on the on-premise Exchange server and run the following command to update the RemoteRecipientType attribute of the local Active Directory User.

Set-ADUser -Identity ((Get-Recipient <PrimarySmtpAddress>).samaccountname) -Replace @{msExchRemoteRecipientType=100;msExchRecipientTypeDetails=34359738368}

Replace <PrimarySmtpAddress> with the primary email address of the mailbox you converted in Microsoft 365.