How to Convert Inactive Mailbox to Shared Mailbox in Office 365?

If you’ve deleted a user in Microsoft 365 and their mailbox is now inactive, but the data is still needed for team access, the best solution is to convert inactive mailbox to shared mailbox in Office 365. I’m here to guide you through the process step by step.

What is an Inactive Mailbox?

An inactive mailbox is created in Microsoft 365 when a user’s account is deleted after a Litigation Hold or a Microsoft 365 retention policy is applied. This preserves the mailbox contents for future access, but you can’t log in to it like a regular mailbox.

Why Convert Inactive Mailbox to Shared Mailbox in Office 365?

Here are the main reasons to convert an inactive mailbox to a shared one:

• Shared mailboxes don’t require a license.
• Multiple users can access and search the data.
• Especially useful in legal or operational follow-ups.
• Inactive mailboxes aren’t searchable from Outlook/OWA until converted.

Prerequisites Before You Start

Here’s what I always ensure before beginning:

• Require an active license for the conversion, as without it, you can’t convert an inactive mailbox.
• The inactive mailbox must be under a Litigation Hold or Retention Policy.
• The Exchange Online PowerShell module setup is required.
• Global Administrator or Compliance Administrator rights required.

How to Convert Inactive Mailbox to Shared Mailbox in Office 365 Step by Step (Manually)

There’s no native GUI method in the admin center. The entire process has to be done via PowerShell, and the steps are as follows:

Step 1. Connect to Security & Compliance Center

Connect-IPPSSession

Step 2. Find the inactive mailbox

Get-Mailbox -InactiveMailboxOnly | ft DisplayName,Identity

Step 3. Since you can’t directly convert an inactive mailbox, create a new shared mailbox and restore the content into it:

New-Mailbox -Shared -Name "Shared_Sales" -DisplayName "Sales Shared Mailbox" -Alias "sharedsales"

Step 4. Use the Restore-Mailbox cmdlet to bring over content from the inactive mailbox into the shared one:

Restore-Mailbox -Identity sharedsales -RecoveryMailbox "<Inactive Mailbox GUID/Identity>" -RecoveryMailboxFolder "Restored"

Step 5. Now assign access to users who need to manage or view this mailbox:

Add-MailboxPermission -Identity sharedsales -User name@company.com -AccessRights FullAccess -InheritanceType All

Step 6. (Optional) Remove the Litigation Hold

Set-Mailbox -Identity "<Inactive Mailbox GUID>" -LitigationHoldEnabled $false

How to Convert Inactive Mailbox to Shared Mailbox In Office 365 (Automatically)

If you’re looking for a way to convert an inactive mailbox to a shared mailbox without using PowerShell manually, I suggest opting for the SysTools Office 365 Migrator.

 Download Now  Purchase Now

This allows you to select the inactive mailbox as the source and migrate it straight to a shared mailbox. Additionally, it ensures full data integrity, maintains folder structure, and provides built-in filters and progress tracking.

Why I recommended this over PowerShell:

• Migrate inactive mailboxes directly to shared mailboxes in Office 365
• No need to restore manually using PowerShell
• Supports bulk migration using admin credentials
• Applies advanced filters for selective mailbox migration
• Maintains folder structure and metadata during the transfer
• Offers real-time progress tracking and detailed migration reports

So, download its free version now, and convert multiple inactive mailboxes in minutes.

Also Read: Add Rules to a Shared Mailbox in Office 365: Detailed Steps

Step-by-Step Instructions that I Followed

After downloading it, follow the steps to convert inactive mailbox to shared mailbox in Office 365 directly:

Step 1. Open the solution, and press the Microsoft 365 options for both source & target platforms.

Step 2. Scroll down, and choose the data category to migrate.

Step 3. Mark these two options if needed: Migrate Document Permissions & User Group Mapping.

Step 4. Afterwards, leverage a date filter option to transfer only relevant data (optional). 

Step 5. Enter the source Admin credentials and validate them. Do the same for the destination platform.

Step 6. Now, add users from the source account using the Fetch Users, Import Users, or Download Template options.

Step 7. After validating all the permissions, hit the Start Migration button.

Related: How to Migrate Shared Mailbox to Office 365?

Author’s Verdict

I always recommend converting inactive mailboxes to shared ones if the data is still needed. It’s a secure, cost-effective way to retain historical information without needing a license. Microsoft doesn’t offer a solution to convert inactive mailbox to shared mailbox in Office 365, but PowerShell and the specified automated solution will help.