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Identify Data to be Migrated and Method - Exchange Mailboxes

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1h 10m

Microsoft 365 represents a combination of Office 365, Windows 10 and Enterprise Mobility offerings – providing the most complete set of SaaS technologies that Microsoft has to offer. With Microsoft 365, organizations can deploy a complete solution encompassing both devices and applications, along with applying security and compliance policies to protect the entire suite.

This course will help you as you plan your migration of users and data to Microsoft 365, including planning your identity and authentication solution, and the on-premises infrastructure needed to support your migration. We’ll also help you understand and identify your business requirements and use cases, to help drive your decision-making process when planning to transition your infrastructure to the Microsoft cloud. We’ll spend some time focusing on networking and discuss some of the networking decisions that need to be made to ensure an optimal migration experience, as well as the best experience for your users after migration.

This course will also help you to identify which data needs to be migrated to the cloud, and what the best migration method will be based on your scenario – we’re also going to cover the different types of user identities, how your users will authenticate, and how that’s going to affect your migration planning.

In addition to talking about these different components, we’re also going to run through a few demos – showing you some of the practical steps involved, along with some tips and tricks we’ve picked up along the way. 

Learning Objectives

By the end of this course, you should be able to:

  • Plan a Microsoft 365 Implementation, including the supporting infrastructure
  • Plan your identity and authentication solution, both on-premises and in the cloud
  • Identify your users, data, and mailboxes to be migrated to Microsoft 365
  • Plan the migration of your groups and user data to Microsoft 365

Intended Audience

This course is intended for people who:

  • Want to become a Microsoft 365 administrator
  • Are preparing to take the Microsoft’s MS-100 exam 


To get the most from this course, you should have a general understanding of networking & server administration as well as IT fundamentals such as DNS, Active Directory and PowerShell.


When you begin to look at the types of data you want to migrate, you'll see that each service has its own native tools as well as numerous third-party tools for performing migrations. There are a few quality third-party tools out there, but I tend to rely on the native tools built into the different technologies, and for the most part, do all that I need to with these tools. That's not to say that you won't have scenarios where a third-party tool will do the job best, but we'll focus on the Microsoft migration tools during this course. 

Migrating mailboxes from Exchange on premises makes up the majority of the migrations that I perform, and the integrated tools and processes for Exchange migrations are well documented and for the most part, work very well. There are three different email migrations that can be made from Exchange server, and the option you choose will be based on several factors. 

First up, is a cutover migration. Microsoft's recommendation is to use this type of migration when you're running Exchange 2003, 2007, 2010 or 2013, and if you have less than 2000 mailboxes to migrate. However, this is only a guideline and not necessarily the best approach to take. A cutover migration is also considered a big bang approach, as all users are migrated at once, and then cutover to Exchange Online at the same time. Migrating more than 100 to maybe 150 users this way is going to require a lot of time and potential headaches as well as potentially a lot of time spent troubleshooting issues with what could be many users at the same time. I would typically only consider a cutover migration when there are a small number of users, and it's not worth going through the extra effort to setup an Exchange hybrid configuration. 

Next up would be a staged migration. Microsoft recommends using a staged migration when you have more than 2000 users and you're migrating from Exchange Server 2003 or 2007. You'll note that this leaves a small set of circumstances that would make you want to lean towards this migration type. When performing a staged migration, you'll do multiple migration batches rather than a single cutover, and you must convert your on-premises users to mail-enabled users after the migration and set their target address to an email address that's on their Exchange Online mailbox. Usually, you'd use the onmicrosoft.com domain for this routing address, as this domain will not be listed on any of your on-premises mailboxes. In both a staged and a cutover migration, you'll need to recreate your users Outlook profile, and neither of these migration types will give you free/busy, or any of the quote distance features you'd expect from a hybrid migration. For these reasons, it's much less common to use cutover or staged migrations, even for smaller organizations. 

The final migration option is an Exchange hybrid migration. This migration type has the most complexity, as it requires your Exchange server to have a public or third-party certificate and requires you to make some firewall changes to ensure that Exchange Web Services and secure mail flow between Exchange Online and Exchange on premises works correctly. You'll also need to have Autodiscover published externally, and optimally, Outlook Anywhere as well. Once you have these pre-requires in place, Exchange hybrid is configured by using the Hybrid Configuration Wizard. This wizard has greatly simplified the process of creating a hybrid environment over the years, and now also includes options for minimal hybrid and an express migration. 

Minimal hybrid will give you the ability to move mailboxes using the Mailbox Replication Service, or to do MRS moves, without giving you secure email between on prem and the cloud and free/busy. An Express migration adds to the minimal hybrid configuration by allowing you to follow basically the same process as a cutover migration without having to reconfigure Outlook profiles. Minimal hybrid would also be a much better candidate for medium sized organizations that would've chosen a staged migration, but without the headaches that I mentioned earlier. Ultimately, the hybrid configuration wizard continues to evolve and get better and better for multiple migration scenarios, making cutover and staged migrations a less likely approach to getting your mailboxes to Exchange Online. 

It's worth noting two other supported ways of migrating email into Exchange Online, which, although typically only used in very specific scenarios, are still good to know about. Exchange Online also supports IMAP migrations from other mail systems. IMAP migrations are generally used when migrating from non-Exchange email systems and will only migrate email messages. You're still required to manually configure Outlook profiles and will also need to manually migrate contacts and calendars. The final migration method in Exchange Online is the PST import service. We'll talk a bit more about this further down, but it essentially allows you to either export your mailboxes from Outlook to PST files and then import them to existing mailboxes in Exchange Online. As you expect, this is a data only migration and there's nothing around mail flow or creating Outlook profiles. All of this is manually done, and the only automation is the import and distribution of these PST files. 

For more information on the different migration types and how they work, take a look at the docs.microsoft.com site, under mailbox migration.

About the Author

Jeremy Dahl is a Senior Technology Consultant who has spent the last 8 years focusing on Microsoft 365 technologies and has been an Office 365 MVP for the last 6 years. Jeremy is a self-proclaimed cloud addict who architects technology solutions that combine cloud technologies with on-premises solutions, allowing organizations to make the most of their existing infrastructure while still taking full advantage of the agility and scalability of what the cloud has to offer.

Jeremy can be found blogging about Microsoft 365 technologies on his website, masterandcmdr.com, and evangelizing the Microsoft cloud on Twitter.