Migration from one M365 tenant to another

We all enjoy how easy it is to work with Microsoft Office 365 where all many thing are automated and taken care of by Microsoft, but one day that you split your company or acquire another one, you will be faced with the need to move data from one Office 365 tenant to another. This is in fact very complex task and is where you will need a much deeper expertise on how things work under the hood.

Let's see what the choices of a migration path are:

1. 1. Use^3rd party tool such as BitTitan or AvePoint. This is quite popular choice and it was the only choice in the past. You will have to pay for each account to be moved.
   2. Use Microsoft free tools. This one is new and we will cover it in the following sections.

From our experience the data move is just one piece of the puzzle. In most cases you need to move DNS domain, so this is big bang migration and all the challenges related to that. On Monday morning we need to reconnect all users to new tenant and it depends on device type, OS, Office version, Active Directorya simply the number of users that need to change profiles day after go-live. No tool can completely liberate you from this painful exercise.

Typical phases of a migration:

• Study phase (Proof of concept, architecture, explore context, tools choice, scoping)
• Prepare (setup environments, pre-stage data move)  
• Communication to users
• Migration event (cutover weekend)
• Post-migration

Read more at https://docs.microsoft.com/en-us/microsoft-365/downloads/microsoft-365-tenant-to-tenant-migration.pdf?view=o365-worldwide

Cross tenant Mailbox Migration

Microsoft provides as a preview a new method called "Cross tenant Mailbox Migration". Refer to https://techcommunity.microsoft.com/t5/microsoft-365-blog/cross-tenant-mailbox-migration-in-now-in-public-preview/ba-p/1692465

Note that it can only migrate Mailboxes, it does not cover Teams, Sharepoint, OneDrive, Groups, etc. It requires Azure Key Vault and Storage Account - for that on top of Office 365, you will need Azure subscription in Target tenant. But do not worry it will not consume a lot. Let's highlight the method used by the tool and them we will explain steps on how to use it.

Microsoft method is based on mailbox Exchangelike migration. You need to create mail enabled user (MEU) in the target, then run migration and the system will copy the data, keep data in sync - one a day, until you finalize the migration (on a D-day say 2 week later). After that new mailbox will be available on the target tenant. Note that on the source the mailbox will disappear and will be converted to MEU. If email will be sent to old MEU, it will be forwarded to new mailbox. Important difference, as^3rd party tool typically have two mailboxes that are synchronized but both still exists. In Microsoft way, one mailbox exists at a time another one is a MEU contact. One another prerequisite for Microsoft method is related to AD synchronized tenants. In order to create MEU you need to have a Exchange hybrid or at least Exchange AD schema in target AD domain/forest. For^3rd party typically it is not required.

The Azure Key vault will keep the credentials (certificate) and Azure storage is just a blob to be used as transfer space. Storage can be any local storage with no redundancy, hot access only - the only this to remember is to keep Key Vault and Storage in the same region.

Once prerequisites are satisfied you can run a powershell oneliner prepared by Microsoft to configure target tenant. Then you will need to give Admin consent in both tenants (url will be provided by a script or will be sent by email). And finally run another oneliner for source. Now you can migrate your users by batches in the same way as you did in the past in Exchange on-premises, or using powershell New-MigrationBatch.

We noticed in out tests that Microsoft method is 1.12 time faster that^3rd party tools. Remember - it is a preview, so do not expect a good support from Microsoft yet.

Mover.io

You next step might be to migrate users data in OneDrive (essentially it is a Sharepoint Online). It can be done by Mover.io (acquired by Microsoft) https://mover.io/guides/migrating-office-365-to-office-365/#introduction

Mover.io provides an easy to understand GUI to move data. Microsoft is preparing to release Powershell methods to move SharePoint Online data, but the release date in not yet confirmed.

Summary

Microsoft provides Cross tenant mailbox migration tool and combined with Mover.io it gives you building blocks for your migration project. Both methods are free of charge, excluding the need for Azure components, and it makes it very attractive choice for fast mass data migration from one tenant to another. Our recommendation at this point in time is to keep 3rd party tools for real life projects until a moment Microsoft moves from Preview to General Availability. Regardless of the tool used to move data, do not underestimate the stress of changing user profiles to connect to new tenant after data is moved.