Office 365 Hybrid Exchange Migration | What is it

Are you interested in taking advantage of Microsoft’s Office 365 Offering, without losing your on-premises infrastructure? You may need Office 365 Hybrid Exchange deployment. Through a hybrid deployment, you can integrate online Microsoft Exchange with its on-premises counterpart. Without 3rd party software tools there will be more to manage, but the benefits can be enormous (more on this below). Here’s everything you need to know about a Hybrid Microsoft Exchange solution.

What is Hybrid?

Under a Hybrid solution, cloud services (such as Exchange Online, SharePoint Online, and Skype for Business) are paired with on-premises solutions like Active Directory, and their own on-premises counterparts. These solutions are able to deliver the benefits of both on-premises and cloud-based services, and can be customized to your organization’s need. An Exchange hybrid deployment allows you to choose where data resides and why allowing for optimized solutions, wherein businesses are able to develop their solutions in the way that works best for them. The majority of organizations deploying hybrid believe they will operate in hybrid mode for the foreseeable future indicating how strategic it is becoming.

With a hybrid solution, a single on-premises Exchange Server will need to remain on the local network. The Office 365 system defers some things to on-premises Exchange Servers, and some tasks that are performed by the on-premises machine and are not moved up to the cloud-based version of Office 365. Features such as “free busy” will be integrated into each platform.

Requirements for Hybrid Deployment

Before initiating a hybrid deployment, look at your current environment and make sure that it meets the following basic requirements:

  • Minimum of one (1) on-premises Microsoft Exchange Server. Microsoft provides a free license for this single server depending on how your Azure/Office 365 tenant is licensed. (More information here.)
  • The Exchange 2013 Hybrid Server must be CU1 with v15 Exchange on-line tenant. This holds true for this scenario because they are required to have coexistence with Exchange 2013.
  • Exchange 2010 Hybrid Server must be SP3 with v15 Exchange on-line tenant. This means upgrading all your Exchange 2010servers to SP3, if it is your current on-premises solution.
  • Existing Exchange 2007 Servers must be SP3 with Update Rollup 9 or later. (Cayosoft recommends you upgrade any 2007 or 2010 servers to 2016 or 2019 for compatibility reasons.)
  • Active Directory forest must be Windows Server 2003 forest functional level or higher.

Whether you have Exchange 2010 or Exchange 2007, it’s likely that you will need to update it to the latest version. Make sure that your Exchange version and Office 365 will integrate properly by keeping everything up to date.

Documentation and Planning

A lack of documentation and improper planning can lead to time-consuming misconfiguration and costly re-work. If you don’t want to drive up the costs of your project, you need to plan for it in advance. A hybrid deployment is more complex than either an on-premises or cloud-based deployment, but it nevertheless has a lot to offer in terms of utility, versatility, and scalability.

A Microsoft Exchange hybrid deployment can be completed in many ways, but it depends on the current environment and requirements. Utilize the Office 365 Deployment Readiness tool for an analysis of your current on-premises environment; it will let you know whether there are changes to be made before you move to an Office 365 deployment.

The recommended migration option is an Exchange Hybrid Migration. While the initial deployment is more complex than other migration options, the benefits outweigh the advantages. Hybrid deployments offer the most robust coexistence between mailboxes residing on premises and those that have already been migrated, providing superior mail flow. There are also tools that you can use, such as the hybrid configuration wizard, and Azure ad connect — these tools can be used to facilitate some of the more complex parts of the migration.

Regardless of the type of migration solution decided upon, it’s best to deploy in a test or lab environment before pushing these changes live. A test will reveal any issues with the Office 365 tenant accounts, Exchange admin center, or other critical features.

Managing Two Environments

Once your hybrid deployment is complete, you will find that managing the two environments may not be as seamless as expected. This can impede help desk and day-to-day administrators from being able to address requests in a timely fashion. Unfortunately, without 3rd party tools, help desk will often escalate “hybrid” tasks to the Microsoft Exchange Service Owner. Implementing a 3rd party tool set or providing other means for the help desk to accomplish their tasks will prevent the Microsoft Exchange Service Owner from going completely mad.


From opening the proper ports on-premises to running the Microsoft Hybrid Exchange Setup Wizard a hybrid migration is always complex, but worth it. Working with a 3rd party tool vendor, like Cayosoft, will help. 3rd party tools not only eliminate scripting, but they also provide valuable functionality that the Microsoft Native Tools simply do not provide. These tools will ensure your Hybrid deployment runs smoothly for your organization and readily integrate Office 365 functionality quickly into your existing on premises Active Directory based environment.

Are you ready to switch to a hybrid solution? Contact Cayosoft today to get started.

Check out these relevant resources.

New Survey Finds...

Active Directory forest recovery not taken serious enough. See what else your peers had to say.