Migrate Shared Mailboxes Between Office 365 Tenants: Admin’s Guide

It must be noted that unlike primary user mailboxes, shared mailboxes have delegated permissions, Send As rights, shared calendars, archives, and collaborative access patterns. If you don’t have a planned migration, then it can result in duplicates, broken permissions, missed folders, and extended disruptions in the business. 

Top Factors to Migrate Shared Mailboxes Between Microsoft 365 Tenants

Some of the popular business scenarios that demand users to transfer shared mailboxes are:

• Mergers and acquisitions
• Divestitures and rebranding
• Tenant consolidation and restructuring
• Domain and brand changes/relocation
• Compliance and Microsoft standardization

In all of these situations, migration becomes critical. It is also due to the fact that this migration involves more than copying mailboxes. This involves emails, folders, hierarchy, permissions, delegates, shared calendars, archive mailboxes, compliance settings, metadata, etc. The reason this matters is:

• Preservation of historical records and communications 
• Departmental data organization and continued workflow
• Long-term data retention and meeting compliance needs 

Prerequisites for Shared Mailbox Migration Without Data Loss

In order to have a secure and successful cross-tenant migration Microsoft 365 shared mailboxes, you need to fulfil this checklist:

• Gather all shared mailbox names and aliases 
• Document their size and locate archive mailboxes 
• Verify admin roles and check available licences 
• Validate domains and check DNS readiness
• Record permissions for Send As and Send On Behalf
• Plan pilot test migration batches and prepare cutover 

Manually Migrate Shared Mailboxes Between Office 365 Tenants

There are two methods for you to perform the shared mailbox migration. The first one is using Microsoft Exchange, and the other one via Outlook/PowerShell. We will discuss each one of them in detail as follows:

1) Exchange Online Microsoft 365 Shared Mailbox Migration

With the cross-tenant migration features of Microsoft, you can move shared mailboxes between tenants. However, it is suitable only for IT administrators and needs careful planning, permissions, and validation. Steps are:

1. Initially, set up the destination shared mailboxes along with the target tenant.
2. Then, edit the migration settings and cross-trust appropriately. Assign necessary permissions and roles. 
3. Further, establish migration endpoints between both tenants.
4. Also, create migration batches containing the shared mailboxes.
5. Perform the first sync of Office 365 Tenant to Tenant Migration. 
6. Afterward, recreate any delegated permissions for that shared mailbox post-migration.
7. Verify that the mailbox contents, folders, and archive are correct.
8. Finally, complete the final cutover and change email routing if necessary.

2) Outlook Migrate Shared Mailboxes Between Office 365 Tenants

This is another method available, but it is highly technical and needs manual effort. Also, you may need to temporarily convert the shared mailbox to a user account first for migration. Note that you need to assign a licence temporarily, which you can remove after the migration if the mailbox is under 50 GB. Follow these steps:

1. First, open the source tenant and export all the permissions. 

Get-MailboxPermission -Identity “MySharedMailbox” | Where-Object {$_.User -ne “NT AUTHORITY\SELF”}  Get-RecipientPermission -Identity “MySharedMailbox” | Where-Object {$_.Trustee -ne “NT AUTHORITY\SELF”}  Get-Mailbox “MySharedMailbox” | Select GrantSendOnBehalfTo

2. Next, convert your shared mailbox to a primary user mailbox using the command:

Set-Mailbox “MySharedMailbox” -Type Regular

3. Further, assign the licenses. Now, sign in to your Microsoft Outlook with this account. 
4. Export the entire data into the PST file for import into the target shared tenant mailbox later. 
5. Afterward, create a new shared mailbox in the target tenant account with:

Set-Mailbox “MigratedSharedMailbox” -Type Shared

6. Import the PST file into this mailbox on the target tenant via Outlook. 
7. Later, re-map all the Full Access, Send As, and Send on Behalf permissions manually. 
8. In the end, re-convert your source mailbox back to shared or delete it entirely as desired. 

Shortcomings of the Manual Method 

• Permission mismatches resulting in data loss 
• Duplicate emails increase the storage space 
• Large mailboxes (100GB+) face throttling issues 
• Failed migration batches mean extended downtime 
• Slow syncs and folder mapping errors lead to incomplete transfers 
• Licencing conflicts bring in migration interruptions 
• Scheduled disruptions due to calendar permissions loss 
• Auto-mapping is not restored, so double the labor 
• Time-consuming, complex, and no built-in monitoring 

Smartly Migrate Shared Mailboxes Between Office 365 Tenants

Large organizations, businesses, and enterprises often prefer staged migrations or a reliable M365 Tenant Migration Software. This is where SysInfo Microsoft 365 Tenant to Tenant Migrator proves beneficial. It handles dozens or hundreds of shared mailboxes in GBs and TBs, reducing the administrative manual effort. With multiple capabilities and an intuitive GUI, it is suitable for technical and non-technical users on Windows and Mac OS. To understand its working, check out the simple steps below. 

Steps to Transfer Shared Mailboxes Between Microsoft 365 Tenants

1. Launch the Microsoft 365 Migration Software and proceed with Copy Mailboxes. 
   
   
2. Then, enter your Shared Mailbox M365 ID and Authenticate your account. 
   
3. Further, select your mailboxes to migrate and click on Continue to Destination. 
   
4. Afterward, choose the destination mailboxes and map them accordingly. 
   
5. Finally, use the filters that you want to customize results and click Start Migration. 
   

Comparing Solutions to Transfer Shared Mailbox with Emails and Folders

We know that there are multiple solutions out there delivering cross-tenant shared mailbox migration with ease. Here, we present a descriptive comparison of SysInfo with other top 2 solutions trusted by users globally. These are:

This explains the core capabilities of the SysInfo software over the other competitors. Other than this, the other benefits that it offers are:

• Retains all mailbox permissions, structure, and metadata 
• 100% security and zero-downtime data access 
• Handles large-sized mailboxes simply with Graph API
• 24*7 expert support to deal with any complexities 

Whether you have @info, @support, or other mailboxes, every shared mailbox is managed simply with no risks or confidential data leaks. 

Migrate Shared Mailboxes Between Office 365 Tenants Case 

A regional healthcare group was handling a merger during which they needed to migrate around 137 Office 365 shared tenant mailboxes. It had almost 5.5 TB of data that needed to be preserved with no loss or downtime. Using the SysInfo Office 365 Tenant to Tenant Migration Software, they performed automated mailbox mapping and incremental sync migration in minimal time. The results achieved were:

• No delay in mailbox access
• Pilot test ensured trust and consistency 
• No duplicacy and 100% preservation
• Continued business operations 

Ideal Practices for Effective Migration

Migration teams and individuals often face several complexities. To ensure hassle-free transitions, ensure these:

• Don’t make any alterations in the mailbox during the final sync.
• Verify your ‘Send As’ and ‘Send on Behalf’ permissions before moving.
• When migrating large batches, check for Microsoft limitations on speed and processing.
• Pilot test a representative sample of shared mailboxes.
• Generate reports after the end of the migration for audit purposes.
• Keep your source account active until you verify migration was a success.

Summing Up

The migration of shared mailboxes is one of the most critical migrations when transitioning between Microsoft 365 tenants. A successful migration is achieved when the delegated access, folder hierarchies, and data fidelity are preserved while maintaining business continuity. Whether you use Microsoft Exchange Online or MS Outlook with PowerShell, you can migrate shared mailboxes between Office 365 tenants, but upto an extent. An ideal solution to keep everything maintained is through the SysInfo Tenant to Tenant Migration Tool. It is secure, scalable, reliable, and trusted by experts for large-scale professional migrations.

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About The Author:

Simran Bhatia

Simran Bhatia is a technical content writer engaged in writing clear, concise, and SEO-optimized content. With a background in computer science and a passion for writing, I thrive to deliver complex technical content in simple layman terms.