Currently you should be running CU9, which is quite outdated.
Please note that it is always recommended to keep your Exchange server up to date for better support.
Since the latest CU version of Exchange 2016 is CU22, please consider upgrading to CU22 and also install the latest SU to protect your server from attacks.
To get information of the latest CUs and SUs of Exchange, you can refer to this link: Exchange Server build numbers and release dates
What is the next CU I should upgrade to?
I tried upgrading to CU 22, but the install failed
You can go directly to CU22.
Here is a Microsoft tool which would guide you through the upgrade: Exchange Deployment Assistant
Once you enter the required information, it would list the detailed steps to upgrade.
In short, you may need to manually prepareSchema/AD/Domain and install the following prerequisites:
- Net Framework 4.8
- IIS URL rewrite module
- Universal C Runtime in Windows (KB 2999226)
Then install CU22.
In addition, you may also use this script to check if the server is already for upgrade: SetupAssist.ps1
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