CU16 Exchange 2016 – a smooth CU

Exchange CU

We just upgraded to CU16 Exchange 2016. There were no real issues and all went well. This upgrade came with notably fewer issues than CU14 for Exchange Server 2016.

You can view the list of issues this update fixes here:
List of addressed issues

And download the update from Microsoft here:
Link to official download page

Tasks before installing CU16 Exchange 2016:

  • Backup your web.config files where you have modified parameters or have added new keys.

    As we experienced it still only the web.config file in the OWA directory takes over parameters and keys you have modified before. To be safe I recommend backup every web.config file you have ever touched/modified. So you can easily reapply the changes you have made.

  • Disable Check for publisher’s certificate revocation in IE.
  • Make sure you have enough free space on the install drive.
    I noticed from 2010 and 2013 times a recommendation for at least 10GB of free space.
  • Check Auth methods on service directories like Powershell, OWA, and ECP and note the output. Verify it after the CU has been installed against these notes.
  • Switch mailbox databases and put the server in maintenance mode.

Order of install:

  • Install the regular Windows patches ( if necessary )
  • Install CU16 Exchange 2016

The CU installation itself took between 3 and 4 hours on the servers in our environment. On some servers, the install found a pending restart state despite a restart before the install. After a reboot, the install continued from that point.

Experiences after CU16 Exchange 2016 has been installed:

  • We had mailtips disabled. Mailtips were enabled afterward.
  • The web.config files in the following directories have been overwritten. Changes needed to be reapplied.

    Active Sync – [ We have an increased attachment size ] :

    C:\Program Files\Microsoft\Exchange Server\V15\FrontEnd\HttpProxy\sync
    C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\sync

    ECP – [ We have additional keys in place. ] :

    C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\exchweb\ews

    Anyway, I always check the OWA web.config as well:

    OWA – [ We have additional keys in place ] :

    C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\Owa

  • Virtual directories for additional OWA and ECP we have in place needed to be recreated.


If you come with .NET 4.7.2 and want to upgrade from CU12 to CU14 this could be helpful:

Install CU 14 Exchange 2016

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