Keep your communication systems protected while you finish your migration: effective May 1, 2026, Microsoft launches a second six-month Extended Security Update (ESU) period for Exchange Server 2016/2019 and Skype for Business Server 2015/2019.
Summary
- Microsoft introduces Period 2 Extended Security Updates for Exchange Server 2016/2019 and Skype for Business Server 2015/2019
- The new coverage period runs from May 1, 2026 through October 31, 2026 (six months)
- Period 2 is a separate purchase and not an automatic extension of Period 1
- Coverage is limited to Critical and Important security updates as scored by the Microsoft Security Response Center (MSRC)
- No further extensions will be offered after October 2026
What is changing?
On April 15, 2026, Microsoft confirmed a second Extended Security Update period for
- Exchange Server 2016/2019 and
- Skype for Business Server 2015/2019.
Period 1 concluded at the end of April 2026, and Period 2 begins May 1, 2026, ending October 31, 2026.
Period 2 is structured as a standalone contract. Organizations enrolled in Period 1 are not automatically renewed and must purchase the new coverage separately. Customers who skipped Period 1 can still purchase Period 2 directly. You can buy the Period 2 ESU licenses via a Microsoft Enterprise Agreement (EA).
What is the Extended Security Update (ESU) program?
The Extended Security Update program is a paid, time-limited offering that provides Critical and Important security patches for Microsoft products that have already passed their official end-of-support date. ESUs are not a lifecycle extension: affected servers remain out of support, and standard support cases cannot be opened. Updates are distributed privately to enrolled customers only and are not published on the Microsoft Download Center.
For Period 2, the supported builds are Exchange Server 2016 CU23, Exchange Server 2019 CU14/CU15, and Skype for Business Server 2015 and 2019.
Customer benefits
- Reduced exposure to Critical and Important security vulnerabilities
- Additional time to complete migrations to Exchange Server Subscription Edition (SE), Skype for Business Server SE, or Microsoft Teams
- Lower risk of email throttling or blocking by Exchange Online
- Continuity of on-premises communication services during the transition
- Predictable, contract-based security coverage through October 2026
Key elements of Period 2 ESU
- Private distribution of security updates to enrolled organizations only
- Confirmation each Patch Tuesday whether an update was released
- Cumulative coverage: Period 2 updates include any fixes from Period 1 builds
- Dedicated inquiry channel for enrolled customers (ExchangeandSfBServerESUInquiry@service.microsoft.com)
Why Period 2 ESU is relevant (if only temporary)
Many organizations are still finalizing their migrations to Exchange Server SE, Skype for Business Server SE, or Microsoft Teams. Running unpatched, out-of-support servers exposes mailboxes, identities, and communication infrastructure to known and emerging threats.
Period 2 reduces that risk for a defined six-month window. It also helps avoid email blocking by Exchange Online, which Microsoft applies to persistently vulnerable on-premises Exchange servers. After October 31, 2026, no additional ESU coverage will be offered, which makes the next six months a hard deadline for migration planning.
Next Steps
- Review which Exchange Server and Skype for Business Server instances remain in production
- Validate current build levels against Period 2 supported versions (Exchange 2016 CU23, Exchange 2019 CU14/CU15, Skype for Business Server 2015/2019)
- Contact SCHNEIDER IT MANAGEMENT for Period 2 ESU pricing and ordering details
- Update any servers still running pre-October 2025 builds to remove email throttling risk
- Plan migration completion to Exchange Server SE, Skype for Business Server SE, or Microsoft Teams before October 31, 2026
- Monitor Patch Tuesday confirmations from Microsoft once enrolled
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Sources
For the announcement of Microsoft Exchange Server Period 2 ESU, please visit: https://techcommunity.microsoft.com/blog/exchange/announcing-period-2-exchange-20162019-extended-security-update-esu-program/4511603.
For the announcement of Microsoft Skype for Business Server Period 2 ESU, please visit: https://techcommunity.microsoft.com/blog/skype_for_business_blog/announcing-%E2%80%9Cperiod-2%E2%80%9D-for-skype-for-business-server-20152019-extended-security-u/4511619.
For useful software licensing information on Microsoft products, please visit: https://www.schneider.im/software/microsoft/.