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Exchange Server with different versions

Running multiple Exchange Server is what we recommend for High Availability. It will give more freedom when updating Exchange Servers, troubleshooting issues, and more. But, do you need to update Exchange Server CU at the same time on all the Exchange Servers, or can you have a difference between the versions? In this article, you will learn how long Exchange Servers with different versions can be kept.


We have two Exchange Servers in the organization. Both the Exchange Servers are members of a DAG. We like to upgrade from Exchange Server 2019 CU10 to Exchange Server 2019 CU11. Therefore, we will follow the Install Exchange Cumulative Update guide and upgrade to the latest version.

Running different Exchange Server version

After installing the latest Exchange Server CU on the EX01-2019, it looks like this:

  • EX01-2019 runs Exchange Server CU11
  • EX02-2019 runs Exchange Server CU10

Read more: Find Exchange version with PowerShell »

Exchange Server co-existence with different version build numbers

How many days can you run Exchange Server with a different version, and what do we recommend?

Exchange Server version difference

It’s possible to run different Exchange Server versions in the organization. For example, you have a DAG configuration with two different Exchange Server versions:

  • Exchange Server 2019 CU10
  • Exchange Server 2019 CU11

Everything will function, and it will work with different Exchange Server versions in a DAG configuration. But is it recommended? No, it’s not. Instead, we recommend upgrading all Exchange Server versions to the same build.

Note: Keep the Exchange Server versions on the same build numbers. It means that you have to install Exchange Server CU on every Exchange Server running in the organization.

It would be best to keep the differences between CUs as short as possible to prevent unexpected issues. That’s why we recommend installing the updates on the same day. If you want to install the CU on one Exchange Server first and wait it out for a week, this is supported. But don’t wait too long. Update the remaining Exchange Servers within a couple of days or a week and not after months.

Install new Exchange Server version

What if you have an Exchange Server running and want to introduce another Exchange Server? Always install the latest Exchange Server build version on the new server.

You can follow one of the below scenarios:

  • Upgrade the active Exchange Server to the latest version. After that, install a new Exchange Server with the latest version.
  • Install the latest Exchange Server version on the new Exchange Server. After that, update the already running Exchange Server to the latest version.*

*Keep the Exchange Server differences as slight as possible. For example, do the upgrade on the same day or within a week.

Keep reading: Exchange schema versions (up to date list) »


You learned how long to keep an Exchange Server in different versions. It’s best not to have an Exchange Server difference in versions and update all Exchange Servers to the same version. It’s okay if you have to wait for a couple of days because of urgent reasons. But, don’t keep the window for weeks and upgrade Exchange Server to the same build as soon as you can.

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ALI TAJRAN is a passionate IT Architect, IT Consultant, and Microsoft Certified Trainer. He started Information Technology at a very young age, and his goal is to teach and inspire others. Read more »

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