All Exchange 2013 Servers in the Organization Must Have Exchange 2013 Cumulative Update 10 or Later Installed

When you are installing Exchange Server 2016 into an existing organization you may encounter a setup error:

All Exchange 2013 servers in the organization must have Exchange 2013 Cumulative Update 10 or later installed.

Cumulative Update 10 for Exchange Server 2013 is the minimum requirement for co-existence with Exchange Server 2016. However, even if you have upgraded all of your Exchange 2013 servers to CU10 you may still see the error message due to other circumstances such as:

• You have one or more Edge Transport servers in the environment
• An improperly removed Exchange server object still exists in Active Directory

Updating Edge Transport Server Build Details

The Edge Transport issue is the simplest to correct. The cause of this issue is that Active Directory does not update the build version of the Edge Transport when the server itself is upgraded to a newer cumulative update, because the EdgeSync process is one way only.

In my environment this is the version that the Edge Transport server is actually at:

[PS] C:\>Get-ExchangeServer EX2013EDGE | fl *version*


AdminDisplayVersion : Version 15.0 (Build 1130.7)
ExchangeVersion     : 0.1 (8.0.535.0)

In Active Directory it is still displayed as the earlier version that it was running when the Edge Subscription was created.

[PS] C:\>Get-ExchangeServer EX2013EDGE | fl *version*


AdminDisplayVersion : Version 15.0 (Build 1104.5)
ExchangeVersion     : 0.1 (8.0.535.0)

To resolve the issue simply remove and recreate the Edge Subscription. On the Edge Transport server:

[PS] C:\>Get-EdgeSubscription | Remove-EdgeSubscription

Confirm
Are you sure you want to perform this action?
Removing Edge Subscription "EX2013EDGE".
[Y] Yes  [A] Yes to All  [N] No  [L] No to All  [S] Suspend  [?] Help (default is "Y"): y

Confirm
Do you want to remove recipients? You don't need to remove the recipients that have already synchronized to this Edge
server if you will re-subscribe it to the same organization. This would improve the performance of Edge synchronization
 when you re-subscribe.
[Y] Yes  [A] Yes to All  [N] No  [L] No to All  [S] Suspend  [?] Help (default is "Y"): n

On an internal Exchange 2013 server:

[PS] C:\>Get-EdgeSubscription EX2013EDGE | Remove-EdgeSubscription

Confirm
Are you sure you want to perform this action?
Removing Edge Subscription "EX2013EDGE".
[Y] Yes  [A] Yes to All  [N] No  [L] No to All  [?] Help (default is "Y"): y

Then follow these steps to recreate the Edge Subscription.

Resolving Improperly Removed Exchange Servers in Active Directory

If your Active Directory contains Exchange server objects for servers that no longer exist then it is likely that at some stage in the past someone decommissioned a server in your environment without properly uninstalling it. This can be resolved by removing the object from Active Directory.

The supported method for removing an old Exchange server object from Active Directory is to install a new Windows server of the same name and then perform a recovery install of Exchange onto that server. After Exchange has been installed you can then cleanly uninstall the server.

The unsupported method is to use ADSIEdit to remove the server object from the Configuration partition.

My recommendation to you is to use the supported method.