Exchange Server Subscription Edition (SE): Your Guide to CUs, SUs, and Modern On-Premises Exchange

Exchange Server Subscription Edition (SE): Your Guide to CUs, SUs, and Modern On-Premises Exchange

Microsoft Exchange Server Subscription Edition (SE) represents the latest evolution of on-premises Exchange, designed for customers who require or prefer to maintain their mailboxes on their own servers. Released in 2021, Exchange Server SE moves away from the traditional long-term servicing channel (LTSC) model of its predecessors (like Exchange 2019 and 2016) and adopts a more modern, continuous update approach, similar to other subscription-based Microsoft products. This means more frequent Cumulative Updates (CUs) that bring not only fixes but also new features, ensuring that on-premises customers have access to the latest capabilities and security enhancements. Understanding the update cadence, the role of CUs and Security Updates (SUs), and best practices for maintaining Exchange Server SE is crucial for any organization deploying or managing it. This guide will serve as your comprehensive resource for navigating Exchange Server SE updates, providing details on build numbers, release dates, download links, and key considerations for keeping your modern on-premises environment secure and up-to-date. Whether you are migrating from an older Exchange version or managing an existing SE deployment, MedhaCloud offers expert support and services for Exchange Server Subscription Edition.

Understanding Updates for Exchange Server Subscription Edition (SE)

Exchange Server Subscription Edition (SE) has a distinct servicing model compared to previous Exchange versions:

Cumulative Updates (CUs): CUs are the primary mechanism for servicing Exchange Server SE. They are full builds of the product and are released more frequently than the CUs for older Exchange versions (typically twice a year, around March and September). Each CU for Exchange Server SE includes all previously released CUs and SUs, as well as new product features and enhancements. This continuous delivery model ensures that SE customers receive the latest innovations and security patches regularly. To remain in a supported state, Microsoft generally requires customers to be on one of the two latest CUs.

Security Updates (SUs): Security Updates are released as needed to address specific security vulnerabilities. These are typically released as part of Microsoft’s monthly Patch Tuesday cycle. SUs for Exchange Server SE are CU-specific. This means an SU released for a particular CU (e.g., 2023 H1 CU) is intended only for servers already running that specific CU. If your server is on an older CU, you must first upgrade to the CU for which the SU is designed (or a later CU that incorporates those security fixes) to apply that SU.

Hotfixes (HFs) / Interim Updates (IUs): Occasionally, Microsoft may release a Hotfix or Interim Update to address a critical, non-security issue that affects a specific CU. These are less common than SUs and are provided on an as-needed basis.

Lifecycle and Support: Being a subscription product, the support for Exchange Server SE is tied to maintaining an active subscription and staying on a supported CU. Running an unsupported CU (generally older than N-2, where N is the latest CU) can lead to a loss of support and inability to apply the latest SUs.

Latest Recommended Update for Exchange Server Subscription Edition (SE)

To ensure your Exchange Server Subscription Edition environment is secure, stable, and benefits from the latest features, it is crucial to stay on a recently released Cumulative Update (CU) and apply all subsequent Security Updates (SUs) for that CU. As of early 2025, you should aim to be on one of the CUs released in 2024 or the latest available CU in 2025.

For example, if Exchange Server SE 2025 H1 CU (Cumulative Update 6) was released in March 2025, this would likely be the most current CU. Before that, Exchange Server SE 2024 H2 CU (Cumulative Update 5) released in September/October 2024 (e.g., KB5042461) would have been a key baseline.

Key Recommendations for Exchange Server SE:

1. Stay Current with CUs: Plan to install one of the two latest CUs. For instance, if CU6 is the latest, CU6 and CU5 would be the supported CUs.
2. Apply All SUs Promptly: Once on a supported CU, diligently apply all SUs released for that CU. For example, if you are on CU5 (KB5042461), you would apply any SUs released for CU5, such as a hypothetical Nov24SU for CU5 (KB5044062) or Apr25HU for CU5 (KB5050674).
3. Verify with Official Microsoft Sources: Always confirm the latest CU and SU information directly from the Microsoft Exchange Server Build Numbers and Release Dates page (this page includes SE) and the Microsoft Security Update Guide.

For direct access to downloads, CUs for Exchange Server SE are typically available on the Microsoft Download Center. For example, the download for CU5 (KB5042461) might be found at a link like https://www.microsoft.com/download/details.aspx?id=106402. Specific SUs (e.g., KB5044062) would be detailed in their respective KB articles with links to the Microsoft Update Catalog.

Keeping your Exchange Server SE deployment updated is not just about security; it’s also about accessing new functionalities introduced with each CU. If you need assistance with planning your update strategy or executing updates for Exchange Server SE, MedhaCloud’s experts are ready to help.

Comprehensive List of Exchange Server Subscription Edition (SE) Cumulative Updates (CUs)

Cumulative Updates for Exchange Server SE are released semi-annually and are full builds of the product, incorporating previous fixes and new features. Staying on one of the latest two CUs is generally required for support. Below is a list of CUs for Exchange Server SE, with release dates, build numbers, and links to download pages or KB articles. Note that as SE is a continuously updated product, this list will grow over time. Always refer to official Microsoft sources for the most current information.

(Note: Build numbers and release dates for future CUs are illustrative. Always verify with official Microsoft documentation.)

Comprehensive List of Exchange Server Subscription Edition (SE) Security Updates (SUs)

Security Updates (SUs) for Exchange Server SE are critical for addressing vulnerabilities and are released as needed, typically monthly. They are CU-specific. Always consult the Microsoft Security Update Guide for the latest SU information.

Keeping your Exchange Server SE patched with the latest CUs and SUs is fundamental for security, stability, and access to new features. For expert assistance in managing your Exchange SE updates or planning a migration, MedhaCloud’s Exchange specialists are here to support you.

How to Check Your Current Exchange Server Subscription Edition (SE) Build Number

Knowing the exact build number of your Exchange Server SE installation is essential for determining its CU and SU patch level. You can find this information using the Exchange Management Shell (EMS) or by checking file versions.

1. Using Exchange Management Shell (EMS) – Recommended:

   Open the Exchange Management Shell and run the following command:

   powershell Get-ExchangeServer | Format-List Name, Edition, AdminDisplayVersion, ServerRole

   The AdminDisplayVersion property will show the version in a format like Version 15.2 (Build XXXX.X). This build number can be cross-referenced with Microsoft’s official list of Exchange Server build numbers and release dates to identify the specific CU and any applied SUs.

2. Checking File Version of ExSetup.exe:

   You can also check the file version of ExSetup.exe located in the Exchange Server installation path (typically C:\Program Files\Microsoft\Exchange Server\V15\Bin\).

   In PowerShell:

   powershell Get-Command ExSetup.exe | ForEach-Object {$_.FileVersionInfo}

   Look for the ProductVersion or FileVersion property. This provides the most precise build number.

Regularly checking your build number against Microsoft’s published list ensures you are aware of your current patch status and can plan updates accordingly.

Important Considerations Before Updating Exchange Server Subscription Edition (SE)

Updating Exchange Server Subscription Edition (SE) with its regular Cumulative Updates (CUs) and necessary Security Updates (SUs) is key to maintaining a secure, supported, and feature-rich on-premises messaging environment. Here’s what to keep in mind:

1. Subscription and Licensing: Ensure your Exchange Server SE licensing and any required software subscriptions are active and compliant. Access to CUs and support is tied to this.
2. Read CU and SU Release Notes Thoroughly: Each CU and SU comes with detailed release notes and a KB article. These documents contain critical information about prerequisites, new features (for CUs), fixes, known issues, and specific installation instructions. Do not skip this step.
3. Comprehensive Backups are Essential: Before any update, perform full backups:
   • System State backups of Domain Controllers.
   • Complete Exchange server backups (OS, databases, logs).
   • Backups of Exchange customizations (e.g., OWA themes, web.config modifications, third-party integrations). Always verify that your backups are restorable.
4. Test in a Lab Environment: If you have a representative lab environment, always test CU and SU installations there before deploying to production. This helps identify potential conflicts or issues specific to your configuration.
5. Active Directory (AD) Health and Prerequisites:
   • Schema/AD/Domain Prep: CUs for Exchange Server SE may require Active Directory schema extensions, AD preparation, or domain preparation. The CU release notes will explicitly state if /PrepareSchema, /PrepareAD, or /PrepareDomain (or /PrepareAllDomains) are needed. These steps require specific permissions and should be performed well in advance of server updates to allow for AD replication.
   • Ensure AD health (DCDIAG, REPADMIN) is optimal before starting any AD preparation or server update.
6. .NET Framework and Visual C++ Redistributable: Exchange Server SE CUs have specific .NET Framework version requirements (e.g., .NET Framework 4.8 or later) and may require specific versions of the Visual C++ Redistributable package. Ensure these are installed on all Exchange servers before running the CU setup. SUs will inherit the CU’s .NET requirements.
7. Plan for Downtime: CU installations are full product upgrades and will require a maintenance window per server. SUs also typically require a server reboot. Communicate all planned downtime to stakeholders.
8. Update Order in DAGs and Sites:
   • In a Database Availability Group (DAG), always place the server being updated into maintenance mode (StartDagServerMaintenance.ps1 or manual steps).
   • Generally, update Mailbox servers first. Within a site, update non-internet-facing (backend) Mailbox servers before internet-facing Mailbox servers (if you have such a distinction).
   • Update all servers in one AD site before moving to the next.
   • Edge Transport servers (if deployed) are typically updated last.
9. Antivirus Exclusions: Verify that your antivirus software has the correct and up-to-date exclusions for Exchange Server files, folders, and processes.
10. Run as Administrator: Always install CUs and SUs using an account with the necessary elevated privileges (e.g., member of Domain Admins, Schema Admins, Enterprise Admins for AD prep; Local Administrator for server installs).
11. Sufficient Disk Space: Ensure adequate free disk space on the system drive and the drive where Exchange is installed for the update files and the installation process.
12. Third-Party Integrations: Verify compatibility of any third-party applications (e.g., archiving, compliance, anti-spam, monitoring tools) with the new CU or SU.
13. Review Post-Installation Tasks: Some CUs or SUs may have specific post-installation tasks outlined in their KB articles. Be sure to complete these.

By carefully considering these points, you can ensure a smoother and more successful update process for your Exchange Server SE environment. For complex environments or if you require expert assistance, MedhaCloud offers specialized support for Exchange Server SE deployments and updates.

General Installation Guidance for Exchange Server Subscription Edition (SE) Updates

This section provides a general overview of installing Cumulative Updates (CUs) and Security Updates (SUs) on Exchange Server Subscription Edition. Always refer to the official Microsoft documentation and the specific KB article for the update you are installing for the most detailed and current procedures.

For Installing Cumulative Updates (CUs):

1. Preparation: Complete all relevant steps from the “Important Considerations” section (backups, AD health, .NET Framework, AD Prep if required by the CU, etc.).
2. Download CU: Obtain the Exchange Server SE CU ISO file from the Microsoft Download Center (links are usually provided in the CU’s KB article or on the Exchange Build Numbers page).
3. Mount ISO: Mount the ISO file on the Exchange server to be updated.
4. Prepare Active Directory (if required by the CU):
   • Run Setup.exe /PrepareSchema /IAcceptExchangeServerLicenseTerms_DiagnosticDataON (from an elevated command prompt on a server in the same AD site as the Schema Master, or a machine with Schema Admins rights).
   • Wait for AD replication.
   • Run Setup.exe /PrepareAD /IAcceptExchangeServerLicenseTerms_DiagnosticDataON (requires Enterprise Admins rights).
   • Wait for AD replication.
   • Run Setup.exe /PrepareDomain or /PrepareAllDomains /IAcceptExchangeServerLicenseTerms_DiagnosticDataON (in each domain with Exchange servers or mail-enabled objects).
   • Wait for AD replication. (Note: The _DiagnosticDataON switch is for current versions; older syntax might be /IAcceptExchangeServerLicenseTerms. Always use the syntax specified in the CU’s documentation.)
5. Server Maintenance Mode (DAGs): Use scripts like StartDagServerMaintenance.ps1 or manually perform maintenance steps for DAG members.
6. Run CU Setup: From an elevated command prompt or PowerShell, navigate to the mounted ISO directory and run Setup.exe /Mode:Upgrade /IAcceptExchangeServerLicenseTerms_DiagnosticDataON.
7. Follow Wizard/Monitor Command Line: The setup process will perform readiness checks and then proceed with the upgrade. This can take a significant amount of time.
8. Reboot: A server reboot is required after the CU installation completes.
9. Post-Installation Checks: Verify event logs, ensure all Exchange services have started, test mail flow, OWA/ECP access, and confirm the new server build number.
10. Exit Maintenance Mode: For DAG members, use StopDagServerMaintenance.ps1 or reverse manual maintenance steps.
11. Repeat for all Servers: Follow this process for all Exchange SE servers in your organization, adhering to the recommended update order.

For Installing Security Updates (SUs):

1. Preparation: Read the SU’s KB article thoroughly. Perform backups.
2. Download SU: Obtain the .msp (Microsoft Patch) file from the Microsoft Update Catalog (usually linked in the SU’s KB article).
3. Server Maintenance Mode (Recommended for DAGs): While SUs are generally less disruptive than CUs, placing DAG members in maintenance mode is a good practice.
4. Run as Administrator: Right-click the .msp file and select “Run as administrator” or use msiexec /update <PatchFileName.msp> from an elevated command prompt.
5. Follow Prompts: The installation process is usually straightforward.
6. Reboot: Most SUs will require a server reboot to complete the installation.
7. Post-Installation Checks: Verify event logs, ensure Exchange services are running, perform basic functionality tests, and check that the build number reflects the SU installation (often a minor revision increment).
8. Exit Maintenance Mode (if used).

Key Official Microsoft Resources:

• Exchange Server Build Numbers and Release Dates: Microsoft Learn (includes SE)
• Install Exchange Cumulative Updates: Microsoft Learn (principles apply to SE)
• Specific CU and SU Knowledge Base articles.

Adhering to these guidelines and Microsoft’s official documentation will help ensure successful updates to your Exchange Server SE environment.

Troubleshooting Common Exchange Server Subscription Edition (SE) Update Issues

Even with careful planning, issues can sometimes occur during Exchange Server SE updates. Here are some common problems and troubleshooting approaches:

1. CU Installation Failures:
   • Readiness Check Failures: These are common and often point to missing prerequisites. Carefully review the errors. Common causes include:
     • Incorrect .NET Framework or Visual C++ Redistributable versions.
     • Pending server reboot from a previous update.
     • AD preparation steps (/PrepareSchema, /PrepareAD) not completed, not replicated, or failed.
     • Insufficient permissions for the account running setup.
     • Antivirus software interfering with setup.
   • Setup Fails During Installation: Review the Exchange Setup Log (C:\ExchangeSetupLogs\ExchangeSetup.log) for detailed error messages. This log is crucial for diagnosing failures.
   • Rollback Issues: If a CU fails mid-installation, the server might be left in an inconsistent state. Restoring from a backup taken just before the update attempt might be necessary.
2. SU Installation Problems:
   • Error during .msp installation (e.g., “The upgrade patch cannot be installed by the Windows Installer service because the program to be upgraded may be missing, or the upgrade patch may update a different version of the program.”):
     • Ensure you are applying the SU to the correct CU level it was designed for.
     • Run the .msp from an elevated command prompt.
     • A pending reboot from a previous CU or SU might be blocking the installation.
     • Antivirus software could be interfering.
   • OWA/ECP Issues Post-SU: Sometimes, configuration files might not update correctly. Running UpdateCas.ps1 and UpdateConfigFiles.ps1 (located in the Exchange Bin directory) followed by an iisreset can sometimes resolve these. Always check the SU’s KB article for known issues or specific post-installation steps.
   • Services Fail to Start: Check the Application and System event logs on the Exchange server for errors related to specific Exchange services. These logs often provide clues about why a service is not starting.
3. DAG and Database Issues Post-Update:
   • Database Copy Failures/Suspensions: Ensure all servers in the DAG are on the exact same CU and SU level. Mismatched versions can cause replication and failover problems.
   • Content Indexing Issues: Sometimes databases may show ContentIndexState as Failed or Crawling for an extended period. Rebuilding the content index might be necessary in some cases.
4. Performance Degradation: While usually temporary as caches rebuild, if performance issues persist post-update, investigate standard performance counters and consult Microsoft resources or support.

General Troubleshooting Steps:

• Always check Event Logs: Application, System, and specific Exchange Server logs (e.g., under Applications and Services Logs > MSExchange Management).
• Consult Exchange Setup Logs: For CU issues, C:\ExchangeSetupLogs is invaluable.
• Microsoft Tech Community – Exchange: A good resource for seeing if others have encountered similar issues: Tech Community.
• Official Microsoft Documentation & KB Articles: These often list known issues and workarounds for specific updates.

For complex or persistent issues, engaging Microsoft Support or a specialized consultancy like MedhaCloud is recommended. Get expert troubleshooting support for your Exchange Server SE environment from MedhaCloud.

Conclusion: Embracing the Modern On-Premises Exchange with SE

Microsoft Exchange Server Subscription Edition (SE) provides a robust, feature-rich, and continuously updated platform for organizations committed to on-premises email. Its modern servicing model, with regular Cumulative Updates bringing new features and vital Security Updates addressing emerging threats, ensures that Exchange SE can meet the evolving needs of businesses while maintaining a strong security posture. This guide has provided a comprehensive overview of understanding, planning, and applying updates for Exchange Server SE, from CU and SU details to installation best practices and troubleshooting common issues.

The key to successfully managing Exchange Server SE lies in diligent planning, staying informed about the latest updates, adhering to Microsoft’s recommended practices, and maintaining a proactive approach to security and maintenance. By keeping your Exchange SE environment current, you not only protect your organization but also leverage the latest advancements in on-premises messaging technology.

MedhaCloud is dedicated to helping organizations maximize their investment in Microsoft Exchange, whether it’s deploying a new Exchange Server SE environment, migrating from older versions, or providing ongoing management and support. Our expertise ensures your Exchange infrastructure is secure, reliable, and optimized for your business needs. Contact MedhaCloud today to learn how we can support your Exchange Server Subscription Edition journey and help you build a resilient and modern messaging platform.

We invite you to share your experiences with Exchange Server SE updates or ask any questions in the comments below. Staying updated is a community effort!

Further Reading in this Series:

• Migrating from Exchange 2019?
• Upgrading from Exchange 2016?
• Decommissioning Exchange 2013?
• Finally moving off Exchange 2010?