Email Migration Options - Migration vs Coexistence
Email Migration Options - Migration vs Coexistence

In this course, you will learn about Microsoft 365 Messaging Migrations and Deployments.

Learning Objectives

  • Email migration options
  • Migrating from on-premises Exchange environment to Microsoft Exchange Online
  • Coexistence between an on-premises Exchange environment and Exchange Online
  • Migrating from third-party mail solutions to Exchange Online

Intended Audience

  • This course is intended for those who wish to learn about messaging migrations and deployments in Microsoft 365


  • Have a basic understanding of Microsoft 365

Welcome to Email Migration Options. In this lesson, we’ll take a quick look at the two ways that you can get to Exchange Online.

The first option is Migration, which, as you would expect by the name, is the movement of user data from your source messaging system to Exchange Online. In a typical migration scenario, the organization needs, or wants, to move all existing on-prem Exchange mailboxes to Exchange Online without any need for a long-term coexistence between the on-prem Exchange org and Exchange Online. 

Coexistence is the other option for getting to Exchange Online. This term refers to a hybrid Exchange environment. In other words, when you have coexistence, you maintain both the existing on-prem messaging solution AND Exchange Online at the same time. 

While coexistence DOES offer a smoother way to move mailboxes between on-prem mail servers and Exchange Online – often without the end users even knowing it’s happening - it also requires more work for mail administrators to setup and maintain.

I should point out that when using coexistence, organizations can choose to keep some mailboxes in the on-prem messaging systems, while migrating others to Exchange Online. It’s entirely acceptable to maintain long-term coexistence if needed. In other words, coexistence isn’t just a migration strategy. It can be a long-term solution as well, if an organization needs or wants to keep some mailboxes on-prem while moving others to the cloud.

Over the next several minutes, we’re going to take a look at the specific methods for migrating from an on-prem Exchange environment to Exchange Online in Microsoft 365.


About the Author
Learning Paths

Tom is a 25+ year veteran of the IT industry, having worked in environments as large as 40k seats and as small as 50 seats. Throughout the course of a long an interesting career, he has built an in-depth skillset that spans numerous IT disciplines. Tom has designed and architected small, large, and global IT solutions.

In addition to the Cloud Platform and Infrastructure MCSE certification, Tom also carries several other Microsoft certifications. His ability to see things from a strategic perspective allows Tom to architect solutions that closely align with business needs.

In his spare time, Tom enjoys camping, fishing, and playing poker.