As part of a hybrid Exchange server deployment, you also deploy the so-called Hybrid Server(s). The name itself might be a little misleading though. After all it’s not some sort of new Exchange server role, nor is it an Exchange server that you deploy specifically to be able to configure a hybrid environment – at least not if you’re already running Exchange 2010 or Exchange 2013 on-premises.

In fact, once you configure a hybrid environment, every Exchange Server in your environment becomes part of that hybrid deployment and will perform one, or more, functions in that regard. However, when referring to Hybrid Exchange servers, we actually mean the Exchange servers which are directly involved in hybrid functions. More specifically these will be the servers that you select during the Hybrid Configuration Wizard.

Exchange 2003 / 2007

If you have still Exchange 2003 on-premises (shame on you!), than your only option is to deploy at least one Exchange 2010 SP3 server and use that one to setup a hybrid deployment. The reason why you have to use an Exchange 2010 server is because Exchange 2013 cannot coexist with Exchange 2003.

Once you installed the Exchange 2010 server, it is the only server capable of understanding the hybrid logic; and therefore considered to be the Hybrid Server. There’s also another reason why a server would be referred to as your Hybrid Server, but more about that later when we’ll talk about the free Hybrid Server license key.

Hybrid Server License Key

Microsoft offers eligible customers free Hybrid Edition/Server licenses. Yes, indeed: multiple licenses if needed. In fact, you’ll get a single license key which you are allowed to deploy on multiple Exchange servers, for as long as you abide to the license requirements. This allows you to maintain high availability – also for hybrid functionality.

The license requirements tell you that you cannot use these ‘dedicated’ Hybrid Servers for anything else but that: you should not host any mailboxes on them. If you do, you are required to purchase a proper Exchange Server license. Once you assigned a Hybrid License to an Exchange server, that server also becomes a Hybrid Server in the pure sense of the word.

Hybrid Server Placement

When you are doing things by the book, introducing a new Exchange Server version could be a rather disruptive action. First, you have to prepare your environment for it (Active Directory schema updates etc) and then, once you have deployed the server, you are expected to point all client access traffic to it. This means that you will have to consider all the things involved with setting up coexistence. In smaller environments this might be a trivial task, but the larger the environment gets, the bigger the implications might be.

Although I prefer this approach (“by the book”), there are times where this isn’t appropriate. Even more, doing this might cause all sorts of issues which you might want to avoid – especially if you’re just looking for a quick way to move to the cloud. If so, the placement of the Hybrid Exchange can become a game changer.

One approach that I have used in the past is to install the new server into the Exchange organization and provide it with its own hybrid namespace. This hybrid namespace is nothing more than a dedicated namespace for hybrid functionality. By doing so, I prevent having to point client access traffic to the new servers and possibly disrupt my existing environment. I can then use the Hybrid Server(s) only     for mailbox moves, hybrid mail flow etc.

Multiple Internet-Connected sites

One of the tasks of hybrid servers is to facilitate mailbox moves to and from Exchange Online. The endpoint that you use for mailbox moves is normally discovered automatically using AutoDiscover. However, sometimes you might want to use Exchange Servers in a different location to perform the mailbox move. One of the reasons why you would want to do this is because that other server is maybe closer to the mailbox or it might have more bandwidth available.

When you want to use other internet-facing Exchange servers for mailbox moves, you must make sure that the MRS Proxy is enabled on those internet-facing servers. You can enable the MRS Proxy on each of these servers by executing the following command:

Set-WebServicesVirtualDirectory <identity> –MRSProxyEnabled:$true

Secondly, you could specify a new migration endpoint using PowerShell. This will allow you to pick your desired endpoint from the Mailbox Migration wizard as well (see image below). You can create new migration endpoints through PowerShell, using New-MigrationEdpoint cmdlet.

Once you have defined multiple migration endpoints, this is how it looks like in the GUI:

One thing to note here is that – regardless of the amount of migration endpoints you create – the sum of value of the “MaxConcurrentMigrations” attribute for all endpoints cannot exceed 100. The default endpoint (created automatically) will already have that set to 100. So make sure that you modify that first before creating additional endpoints.

The following image depicts the primary endpoint ( and the new secondary (and manually created) endpoint “”:

Alternatively – if you don’t want to create additional endpoints or you plan on using that endpoint only once – you can create the move requests with PowerShell and specify the –RemoteHostname parameter manually.


Either approach outlined above should work just fine. Which one you choose greatly depends on your current deployment and the effort that goes with introducing a newer Exchange version into your environment. Whenever possible, try to take the by-the-book approach as it might save you some headaches further down the road.