Upgrading to Exchange Server SE (Subscription Edition): Paths, Best Practices, and Monitoring

Why You Must Upgrade to Exchange Server SE Before October 2025

Microsoft is ending support for Exchange Server 2016 and 2019 on October 14, 2025, making it essential for IT teams to upgrade to Exchange Server Subscription Edition (SE) to maintain security and compliance.

Exchange Server 2016 End of Support

Exchange Server 2016 (v15.1) reaches end of support in October 2025, leaving systems exposed to security vulnerabilities if not upgraded.

Exchange Server 2019 End of Support

Exchange Server 2019 (v15.2) also loses support in October 2025, creating the same urgency for IT administrators to plan their move to Exchange SE.

What’s New in Exchange Server SE vs Exchange 2019 CU15

The RTM release of Exchange Server Subscription Edition (Exchange Server SE) has been available since July 1, 2025. Basically, installing Exchange Server SE is easy because it's no different from installing Exchange Server 2019, like the CU15 version. That's because Exchange Server SE has the same code as Exchange Server 2019 CU15.

Much has already been written about the few differences between Exchange Server CU15 vs Exchange Server SE. However, for the sake of completeness, I would like to list the three differences here once again:

1. The product name is now simply Exchange Server.
2. The license file provided changes
3. The build number increases to 15.2.2562.17

Upgrade Options for Exchange Server SE

Upgrading to Exchange Server SE is not optional; support for Exchange Server 2016 and 2019 ends on October 14, 2025. The good news is that IT administrators have three upgrade paths, depending on their current environment. Here are those three options available for upgrading to Exchange Server SE.

Option 1 - Exchange Server 2016 CU23 to Exchange Server SE RTM (Legacy Upgrade)

There is a major release change between Exchange Server 2016 and Exchange Server SE. Exchange Server 2016 is version 15.1, while Exchange Server SE, like Exchange Server 2019, is version 15.2. This means that only a classic, so-called legacy upgrade is available.

A legacy upgrade of Exchange Server involves installing and configuring new Exchange Server systems on the latest Windows Server systems. After installation and complete setup, you can migrate all mailboxes and features from Exchange Server 2016 to Exchange Server SE. The most important tasks include:

• Installing and configuring the operating system, ideally Windows Server 2025, by the recommendations for Exchange Server 2019 and SE
• Setting up the required data drives and mailbox databases, including a new database availability group (DAG)
• Installing the TLS certificate and configuring the Exchange namespace
• Configuring Exchange Server security best practices
• Checking the installation and configuration using the HealthChecker PowerShell script
• Move all mailboxes and adjust mail routing

After completing the move, it is essential to uninstall the old Exchange Server 2016 installations cleanly. This is the only way to ensure that configuration remnants in the Active Directory configuration partition do not cause unwanted side effects during operation.

Option 2 - Exchange Server 2019 CU14/15 to Exchange Server SE RTM (Legacy Upgrade)

If you are currently running Exchange Server 2019 CU14/15 on Windows Server 2019, you can easily perform an in-place upgrade as described in option 3. However, Windows Server 2019 has been in extended support for more than a year and a half. You should therefore consider whether a more recent Windows Server operating system would be a better choice. The server hardware you are using may also have exceeded its performance horizon.

By installing a new Windows Server 2025 system, you are setting the course for a secure future for your Exchange organization. This automatically puts you in the same situation as in option 1. You will need to put new server systems into operation, install Exchange Server SE, and perform all the above steps mentioned in Option 1 to migrate the mailboxes.

Operating Exchange Server with a legacy upgrade is very easy. All Exchange Servers can be members of the same load balancer application pool. Regardless of the location of the mailbox, each Exchange Server addressed by the load balancer establishes a proxy connection to the appropriate server. This applies to both variants 1 and 2.

Option 3: Exchange Server 2019 CU14/15 to Exchange Server SE RTM (In-Place Upgrade)

This upgrade option is the simplest, most convenient, and most secure form to upgrade to Exchange Server SE. Installing Exchange Server SE RTM on, for example, an Exchange Server 2019 CU15 system with August 2025 HU results in an upgrade from build 15.2.1748.36 to 15.2.2562.17.

As you can see, there is no major release change from Exchange Server 2019 to Exchange Server SE. Both versions are so-called 15.2 builds. It is precisely this fact that makes an in-place upgrade possible in the first place.

Even if your Exchange Server 2019 systems are currently running on Windows Server 2019, an in-place upgrade may be the best option for you to address the end of support for Exchange Server 2016 and 2019 on October 14, 2025. By installing Exchange Server SE, your IT infrastructure will be on the safe side for the time being. You can plan a legacy migration to Exchange servers with a newer operating system later and implement it at your leisure.

Why Exchange Monitoring Is Critical Before, During, and After the Upgrade

Regardless of whether you have hybrid or purely on-premises environments, continuous monitoring of Exchange servers is necessary to ensure system performance and security.

Common Issues Without Monitoring

Without Exchange monitoring, IT teams often miss early warning signs of:

• Delayed mail delivery
• Database storage pressure
• Performance bottlenecks
• Potential security risks

Benefits of Proactive Exchange Monitoring

Professional monitoring provides the necessary transparency and enables early detection of incidents before they cause disruption and impact users.

• Detect issues before they disrupt users
• Proactively secure Exchange infrastructure
• Reduce downtime and IT help desk escalations

ENow Exchange Monitoring & Reporting Solution

Solutions like ENow’s Exchange Monitoring & Reporting provide real-time visibility into system health. Unlike Microsoft's native admin tools, ENow delivers actionable alerts, performance dashboards, and reporting transparency.

Conclusion – Choose the Best Upgrade Path + Secure Your Exchange Environment

There is no single recommendation that represents the right upgrade to Exchange Server SE, as every Exchange environment is different and has different requirements. However, what they all have in common is that if you still need to implement a local Exchange Server organization, you must upgrade to Exchange Server Subscription Edition.

The in-place upgrade from Exchange Server 2019 CU14/15 to Exchange Server SE is the simplest and fastest option. Professional monitoring plays a crucial role in the smooth operation of Exchange systems. Continuous monitoring allows potential risks to be identified early on and addressed accordingly.

Exchange monitoring tools such as those offered by ENow enable targeted and efficient management of Exchange servers, thereby contributing significantly to ensuring stability and security during operation.

These measures lay the foundation for future-proof and reliable email communication in your company. You can plan the next steps with peace of mind – your infrastructure is already well equipped with the upgrade to Exchange Server SE.

Additional Resources & Sources

• Exchange Server 2019 and SE System Requirements
• Exchange Server Subscription Edition (SE) is now available
• Why “in-place upgrade” from Exchange 2019 to Exchange SE is low risk
• Security best practices for Exchange Server
• Exchange Server Health Checker