Microsoft has dropped out Service pack model and start using cumulative updates (CU) while back.
You can read more about it on this article. If you are not on the latest CU , most of the last living on premises clients will not be wanting to implement latest CU on their on prem Exchange Servers, due to it is buggy reputation. Remember how many times newest CU broke Exchange more than it claimed to fix. You need to make sure .NET frame work is supported by the version of Exchange + CU version you have. Very recently, I have encounter interesting finding, what MS is recommending. Here is an example, you are running E2016 on prem with CU7 and wanting to go to CU8, and the latest CU version is CU9. MS did recommend CU8 has caused so many issues therefore CU9 is more applicable. At the time this article is written, there are no known major issues with CU9.
This year July the 1th upcoming CUs will require .NET 4.7.1, so you would think your upgrade logic will tell you install CU9 then upgrade .NET to 4.7.1. Since .NET 4.7.1 is not supported by CU7 installing it first would cause issues? I thought so as well. The recommended update path for those who are on E2016 & CU7 is Install .NET 4.7.1 first, reboot, then install CU9 (assuming you wanted to skip the buggy CU8)
I found this interesting and worth for mentioning about it. You can read similar verbiage on the .NET section of this article if you need MS backing.
https://technet.microsoft.com/en-us/library/ff728623(v=exchg.150).aspx
Oz Casey, Dedeal
Principal Systems Engineer
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