What Is a Cumulative Update (CU) for Exchange Server 2019?
A Cumulative Update (CU) for Microsoft Exchange Server 2019 is a complete, full build of Exchange that includes:
- All previous fixes and improvements from earlier CUs, and
- New fixes, features, and compatibility/support changes.
You can think of each CU as a “new snapshot” of Exchange 2019. If you install the latest CU, you automatically get everything that was included in all the older CUs.
Key idea: A CU is cumulative. You don’t stack them one-by-one; each one already contains all the earlier ones.
After the First Exchange 2019 Server Is Installed
Once your first Exchange Server 2019 is installed and working:
- You should plan a regular schedule to keep Exchange updated with the latest CUs.
- All additional Exchange 2019 servers you add to the organization should be installed directly with a modern CU (ideally the latest one).
- Microsoft support normally only covers the latest CU and sometimes the previous one, so staying close to current is important for support and security.
Practical tip: When you build a new Exchange 2019 server, don’t install the “original” version and then patch it. Download the latest CU and install Exchange directly from that CU media.
What Are the Monthly (or Frequent) Updates For?
Even after installing a CU, you may see monthly updates such as:
- Security updates (SUs)
- Critical hotfixes
- Other Windows/OS patches that affect Exchange
These monthly updates:
- Fix newly discovered security vulnerabilities.
- Address stability and reliability issues found after the CU was released.
- Keep your server in a supported and secure state.
In short: the CU brings you to a certain “base level,” and the monthly updates keep that base level secure and stable until the next CU is released.
Do I Need to Install Every CU in Order?
No, you can skip directly to the latest CU.
Because CUs are cumulative, there is no need to install them one by one. If you are on, for example, CU10 and the latest is CU15:
- You do not have to install CU11, CU12, CU13, and CU14 first.
- You can go directly from CU10 to CU15 in a single step.
Example: “I’m on CU13 and missed CU14. Can I install CU15 directly?”
Yes. Just install CU15. It already contains everything from CU14 and earlier.
Do I Need to Install “Master” CUs in Order?
No, just install the latest supported CU.
Sometimes admins think they must go through every “major” or “master” CU in order (CU1, CU2, CU3, etc.). This is not required.
- Each CU is self-contained and already includes all fixes and changes from previous CUs.
- Best practice is to go directly to the latest CU that Microsoft supports for Exchange 2019.
There are only a few things to keep in mind:
- Always read Microsoft’s release notes for that CU (prerequisites, schema changes, .NET/Windows requirements, known issues).
- Make sure your Windows Server OS and .NET version are supported for the CU you’re installing.
- Plan a proper maintenance window and back up your Exchange and OS before updating.
Summary
- CUs are cumulative. Each CU contains all fixes and features from all earlier CUs.
- After the first Exchange 2019 server is installed, you should plan to keep it updated with the latest CU plus ongoing monthly security updates.
- Monthly updates (especially security updates) keep your CU base level secure and stable until the next CU.
- You do not need to install every CU you missed. You can skip directly to the latest CU.
- You do not need to follow any “master CU” order. As long as your OS/.NET meet the requirements, you can go directly to the latest supported CU.
If in doubt, check Microsoft’s official Exchange 2019 CU documentation and support matrix, then plan your upgrade straight to the newest CU.