Convert Linked Mailbox to User Mailbox

One of the main issues with syncing users to Office 365 is when the user has a Linked Mailbox and this can give you a bit of a headache as IdFix can't pull this kind of information.

This enters into another situation where you cannot know which Mailboxes are LinkedMailbox type and yet you need to ensure that all these mailboxes are of an Office 365 supported type.

In this post I will show you:

  1. How to find linked mailboxes
  2. How to convert in bulk / individually


For this process to work 100% you must have the following access permissions:

  • Exchange Server Recipient Management or Organization Management
  • Powershell at least version 3.0

About Linked Mailbox

What are Linked Mailboxes? Normal mailboxes on Exchange Server are users within that server associated with an AD forest. A Linked Mailbox allows you to deploy Exchange Server in one forest while allowing users in several other trusted forests to associate with a Mailbox on that Exchange server.

Relação de confiança entre florestas com caixas de correio vinculadas, troca de caixa de correio vinculada, caixa de correio vinculada

That is, in a nutshell Linked Mailboxes are mailboxes associated with users outside of your AD forest..

And why is it so important to convert these users to UserMailbox? Because there is no UPN assigned to these users, as they exist only in another forest, so they are handled differently by Azure AD Connect, filtering through synchronization.

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Getting information from Linked Mailboxes

To pull all Linked Mailboxes you have in your Exchange environment you must run the following powershell command:

This command will return a CSV file for you with all mailboxes. Save because we will use more below.

Convert Linked Mailboxes to User mailboxes

After getting your list of LinkedMailboxes you should import and then convert users accordingly.

Done this just wait, your Linked Mailboxes will be converted to UserMailbox.

To convert individually, use the following commands:

How to tell if this worked

You can use the following command to get information from your Mailbox.


By performing this activity you will be meeting one of the Azure AD Connect Requirements for user synchronization. Do your validations first, before starting this process for your entire forest and you will not have many problems.

To the next!

Carlos Oliveira

Carlos Oliveira, 25, founder of CloudSquad, a Cloud Computing content sharing blog where he brings tips and tricks about Office 365 and Azure, and is a hub for bringing practical solutions to complex problems.

Carlos Oliveira
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