Everything you need to know for a smooth upgrade to Microsoft Exchange Server SE

In May 2024, Microsoft shared its updated roadmap for Exchange Server and its plans for the future. On July 1, 2025, the Exchange Server Subscription Edition (SE) was launched, and to ensure a smooth transition, it’s important that businesses and organizations prepare carefully. This guide provides an overview of what you need to consider when planning to upgrade from previous versions of Exchange Server to Exchange Server SE, whether you’re running a fully on-premises environment, a hybrid setup, or are only using recipient administration tools.

We conclude with a FAQ section that answers common questions.

Why upgrade to Exchange Server SE?

Exchange Server SE is a significant milestone for organizations that want to continue running Exchange in an on-premises or hybrid environment. Unlike previous versions, Exchange SE follows Microsoft’s Modern Lifecycle Policy, which means there is no fixed end date for support as long as your environment stays up to date with the latest Cumulative Updates (CUs). This marks a major shift from earlier versions and requires ongoing planning and maintenance to ensure your environment remains secure and compliant.

Support for Exchange Server 2016 and 2019 ends on October 14, 2025, which means no further security updates or patches will be released after that date. Continuing to use these versions after the end of support introduces significant security risks, as new vulnerabilities will no longer be addressed. That’s why it’s critical to begin your upgrade to Exchange SE as soon as possible.

Key considerations for upgrading

1. Upgrade paths

The upgrade process to Exchange Server SE depends on which version of Exchange Server you’re currently using:

• Exchange Server 2019: If you’re already running Exchange 2019 (CU14 or CU15), upgrading to Exchange SE is straightforward and can be done as an in-place upgrade. This means you can install the Exchange SE RTM as a Cumulative Update directly on your existing servers, with no major code changes. This makes the transition relatively low risk.

• Exchange Server 2016: If you’re using Exchange 2016, you must first upgrade to Exchange 2019 before moving to Exchange SE. This requires a traditional migration process, including the transfer of mailboxes (classic mailbox migration). Since Exchange 2016 cannot coexist with Exchange SE CU2 (planned for late 2025), it’s important to plan this upgrade as soon as possible.

• New environments: If you’re building a new Exchange environment from scratch, you can install Exchange SE directly, provided that you meet the system requirements.

Recommendation: If you’re still using Exchange 2016, begin by upgrading to Exchange 2019 as soon as possible to avoid being in a position where you can no longer receive security updates. Once you’re on Exchange 2019, transitioning to Exchange SE will be much easier.

2. System requirements

Exchange Server SE has the same hardware and software requirements as Exchange 2019, which means it can run on Windows Server 2019, 2022, and 2025. Keep the following in mind:

• Operating system: Windows Server 2019 is supported until January 9, 2029, while Windows Server 2022 is supported until October 14, 2031. Windows Server 2025 is also expected to be supported, but always check the latest requirements before installation. In-place operating system upgrades on an Exchange server are not supported, so plan any OS upgrades carefully.

• Hardware: Ensure your servers meet the minimum requirements for Exchange SE, even though many Exchange 2019 servers may run on lower resources. Verify that your hardware is sufficient to handle future updates and performance needs.

3. Licensing

Exchange Server SE introduces a new subscription-based licensing model, unlike previous versions where you could purchase a perpetual license. This means that you must have an active subscription to continue using Exchange SE. Here’s what you need to know:

• Server Licenses and CALs: To use Exchange SE, you need both server licenses and Client Access Licenses (CALs) with active Software Assurance (SA). Alternatively, qualifying cloud subscriptions such as Microsoft 365 E3 or E5 include Extended Use Rights, providing unlimited server licenses at no additional cost. Other Exchange Online plans, such as Plan 1 or Plan 2, may also qualify but always check Microsoft’s Product Terms for the latest details.

• Hybrid environments: If you’re running a hybrid setup with Exchange Online and are only using the on-premises server for recipient management (with no active mailboxes), certain cloud licenses may cover this scenario. Consult a licensing specialist to ensure your setup is properly licensed.

• Costs: Since Exchange SE is subscription-based, organizations will need to budget for ongoing licensing costs, whether monthly or annually. If you’ve previously skipped versions to save costs, that approach will no longer be viable.

Recommendation: Consult a Microsoft licensing specialist or partner (e.g., via contact details such as frank.carius@netatwork.de or 0800NETATWORK) to get a clear understanding of which licenses best suit your organization.

4. Coexistence and migration

Exchange SE can coexist with Exchange 2016 (CU23 or later) and Exchange 2019 (CU14 or later) during a transitional period, but this will change with the release of Exchange SE CU2 (scheduled for late 2025). After CU2, Exchange SE will no longer be able to coexist with Exchange 2016 or 2019, making it important to complete your migration before that point.

• Migration: If you are running older versions, you may need to perform a migration by gradually moving mailboxes to a new Exchange SE environment. This is especially relevant for Exchange 2016 users.

• Security risks:: After October 2025, Exchange 2016 and 2019 will no longer receive security updates. Since Exchange SE and Exchange 2019 share the same codebase, it’s likely that vulnerabilities fixed in SE will also exist in the older versions making continued use a security risk.

Recommendation: Plan your migration to move mailboxes to Exchange SE and decommission legacy servers before CU2 is released to minimize risk.

5. Technical changes

Exchange SE introduces several technical changes that impact administration and operations:

• RPC/HTTP (Outlook Anywhere): Microsoft had planned to deprecate RPC/HTTP, but after receiving customer feedback, this has been postponed. A new timeline will be announced after the launch of Exchange SE. Stay tuned for updates.

• REST API for administration: Exchange SE replaces Remote PowerShell (RPS) with a modern REST-based API for PowerShell commands. This means that provisioning tools will need to be updated after CU1. 

• Skype for Business/Lync-integration: The integration between Skype for Business/Lync and Outlook Web App (OWA) will be removed, simplifying deployment for most organizations.

Recommendation: Test new features, such as the REST API, in a lab or staging environment before implementing them in production.

6. Timeline

Here’s a summary of key dates to keep in mind:

• October 2025: Mainstream support for Exchange 2016 and 2019 ends.
• October 2026: Microsoft’s Extended Security Updates (ESU) program ends, the final date after which no further security updates will be released for these versions.

Recommendation: Start planning your upgrade now to avoid ending up in an unsupported environment.  Reminder: Exchange 2016 and 2019 ESU Program Ends in October 2026 | Microsoft Community Hub

FAQ

Conclusion

Upgrading to Exchange Server SE is essential for organizations that wish to continue using Exchange on-premises or in a hybrid environment. By carefully planning, reviewing licensing requirements, and following Microsoft’s recommendations, you can ensure a smooth transition and a secure environment. Start by evaluating your current setup, upgrade to Exchange 2019 if necessary, and make sure you have the right licenses in place. Reach out to a Microsoft partner or licensing specialist for further assistance.

For more information, see Microsoft’s official guides:

• Upgrading to Exchange Server SE
• Exchange Server Roadmap Update – May 2024
• Modern Lifecycle Policy

Feel free to contact us if you need help with your upgrade!