Exchange 2019 and 2013: Is coexistence possible? Yes, here’s how

Exchange 2010 is now at end of support, but those running it have some options to migrate. As you are aware, you cannot introduce Exchange Server 2019 with Exchange 2010 in the environment — you have to either upgrade to Exchange Server 2013 or Exchange Server 2016. If you are already on Exchange Server 2013 and want to migrate to Exchange Server 2019, there are a few requirements that need to be met or you to do this. If you plan to move to Exchange 2013 and retiring Exchange 2010 and then move to Exchange Server 2019, you can also do that, but most move to Exchange Server 2016 and then to Exchange 2019. Here is a list of things you need to understand that are required — they are not optional — for successful coexistence between Exchange 2019 and 2013. (We have previously discussed coexistence between Exchange 2019 and 2016.) We will discuss each section in more detail:

• Active Directory supported environments.
• Exchange 2013 CU requirements to support the introduction of Exchange Server 2019.
• .NET Framework support in Exchange Server 2013.
• Features not supported in Exchange 2019.

We will now discuss what will work in coexistence with regard to your Active Directory environment.

Active Directory supported environments

I don’t like to be the bearer of bad news, but if you are running coexistence with Exchange Server 2013 and Exchange Server 2019, you cannot introduce Windows Server 2019 domain controllers. I know this is not what you wanted to hear, but Microsoft only supports Windows Server 2016 domain controllers, and this will work with both versions of Exchange. However, you need to be on Exchange 2013 CU5 (SP1) as a minimum to support Windows 2016 domain controllers.

Please do not upgrade your environment and think it will work — it won’t, unfortunately — and you will get some funky errors. Microsoft has a support matrix that clearly outlines what is supported and what not.

You can upgrade your Active Directory forest functional level to Windows Server 2016. This is supported in Exchange Server 2019 and Exchange 2013 from CU5 (SP1)

The next step you need to look at is patching your Exchange 2013 environment, which we will discuss next:

Exchange 2013 CU requirements to support the introduction of Exchange Server 2019

Many admins believe “if it ain’t broke, don’t fix it.” That is often true, but if you want to introduce Exchange 2019 into your environment, you need to upgrade your Exchange 2013 servers. Microsoft only supports the latest two cumulative updates. Anything else is not supported, so if you log a support call, they will ask you to upgrade first.

Exchange Server 2013 has to be on cumulative update (CU) 21 as a minimum for you to introduce Exchange 2019. You can be on CU23, for example, which is fine, but every single Exchange 2013 Server in your environment needs to be upgraded to the CU that is supported. This includes your Edge Transport Servers as well. Again, you can refer to the matrix concerning what versions are supported. This matrix gets updated regularly with new information.

In the next section, we will talk about .NET Framework 4.8 and support for Exchange Server 2013.

.NET Framework support in Exchange Server 2013

.NET Framework has always been a tricky one. When I say tricky, Microsoft only supports certain versions of .NET Framework. If you deployed Windows updates with SCCM or WSUS, there were some instances where a version that is not supported was deployed, and this broke Exchange. If you are on Exchange 2013 RTM or Exchange 2013 CU22, you won’t be able to install .NET Framework 4.8. Only from CU23 for Exchange 2013 can you install .NET Framework 4.8, and if you are running .NET Framework 4.7.2, you are able to upgrade. Please pay close attention to this and ensure that you have a block on deploying .NET Framework in your environment automatically as you don’t want to end up recovering a server because of this.

Features not supported

If you do use Unified Messaging in Exchange 2013, you will need to look at moving this to Skype for Business Cloud Voice Mail as Exchange Server 2019 does not have unified messaging. Exchange 2016 was the last version to have Unified Messaging.

Your roles also change. The client access role in Exchange 2013 is now a service on the mailbox role in Exchange 2019.

Final thoughts on Exchange 2019 and 2013 coexistence

As you can see, there aren’t too many requirements, but you do need to follow what is outlined. If you are planning on moving to Exchange 2016 later and then Exchange 2019, please plan this. You don’t want to be doing so many migrations — it’s just time-consuming. Rather, go straight to Exchange 2019.

If your plan is to have Windows Server 2019 domain controllers, you will need to either migrate everything off Exchange 2013 to Exchange 2019 and then decommission your Exchange 2013 servers. This will then allow you to introduce the newer domain controllers, and then you can also decommission the “older” versions you have in the environment. Or if you decide to build a new Active Directory forest that only has Windows Server 2019 domain controllers and Exchange Server 2019 in that environment, you would need to look at third-party tools to do cross-forest migrations.

Plan your migration carefully. The roadmap for Exchange Server 2019 has some exciting things coming down the line. And be aware: Extended support for Exchange 2013 ends April 11, 2023, and extended support for Exchange Server 2019 ends Oct. 14, 2025.

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