Time’s almost up for Exchange 2016 and 2019: Prepare for Exchange Server Subscription Edition (SE)

Support for Microsoft Exchange 2016, Exchange 2019, and Outlook 2016 ends on October 14, 2025. That includes all security updates, bug fixes, and technical support. If your environment includes any of these versions, now is the time to plan your next steps. 

After the deadline, Microsoft will no longer provide any of the following support services: 

• Help with configuration or troubleshooting 

• Fixes for performance or stability issues 

• Security updates for new vulnerabilities 

• Updates for global time zone changes 

With Exchange Server Subscription Edition (Exchange SE) launching in July 2025, IT teams must choose between two distinct paths. 

• Exchange Online: Microsoft’s cloud-based email platform, ideal for organizations prioritizing scalability, automation, and access to the latest innovations. 

• Exchange SE: The on-premises successor to Exchange 2019, designed for organizations with data residency needs, compliance constraints, or hybrid directory dependencies. 

Each option involves technical prerequisites, licensing considerations, and risks if the transition is delayed. 

What end of support actually means 

For organizations still operating on-premises Exchange 2016 or 2019 servers—or using Outlook 2016 clients—end of support means losing all access to Microsoft’s updates, security patches, and technical assistance. These servers will continue to run, but without protection or compatibility guarantees, they quickly become risky to maintain. 

After October 2025: 

• No security patches or bug fixes  

• No time zone updates or Microsoft support 

• Exchange Online may block mail from unsupported servers 

Delaying migration may lead to deprecated features, TLS handshake failures, and failed MAPI connections. The Client Access Front End in Exchange Online will also start rejecting legacy clients after support ends. 

Microsoft strongly recommends acting now—especially if you're running Exchange 2016. There's no direct upgrade path from Exchange 2016 to SE. A two-step upgrade is required. 

What to do if you're still using Outlook 2016 or 2019 

Outlook 2016 and 2019 will also be out of support by October 2025. These versions rely on outdated authentication protocols (e.g., RPC over HTTP), which are incompatible with Exchange SE and Exchange Online. 

Upgrade recommendations: 

• Replace Outlook 2016 and 2019 with supported clients: 
  

  • Microsoft 365 Apps for Enterprise 

  • Outlook LTSC 2021  

• Use MAPI over HTTP with OAuth 2.0 for secure, modern connectivity 

• Avoid hybrid client issues — legacy clients can break Autodiscover and EWS workflows 

• Note: Legacy signature workflows may stop functioning. This includes outdated tools like Exclaimer’s Signature Manager Outlook Edition 

Exchange Server SE: What’s actually changing 

Exchange SE is Microsoft’s final on-premises release, governed by the Modern Lifecycle Policy. It is built on Exchange 2019 CU15 and offers similar performance. Microsoft is not focusing on new feature development but on lifecycle stability and secure, supported servicing. 

Key changes: 

• No perpetual license model — subscription required via SA or Microsoft 365 

• Biannual cumulative updates 

• In-place upgrade supported only from Exchange 2019 CU15 

System requirements: 

• Windows Server 2019, 2022, or 2025 

• Minimal domain functional level: Windows Server 2012 R2 

• AD schema: unchanged from Exchange 2019 CU15 

Exchange SE retains the modern Exchange Admin Center (EAC). Admins should also become familiar with REST-based workflows, as these will replace traditional PowerShell scripts. 

Technical deprecations in Exchange SE 

Starting with CU1 (expected late 2025), Exchange SE will enforce modern protocols: 

Plan for script updates, orchestration tool testing, and checks to third-party integrations that rely on deprecated features. 

Exchange Toolbox tools like Queue Viewer and Performance Monitor remain supported. However, PowerShell scripts must be rewritten for REST. 

Exchange SE enforces hardened security defaults. If you're still using NTLM or legacy protocols, update authentication methods and validate all mail routing paths. 

Licensing and cost updates 

With the shift to subscription-based licensing in Exchange SE, organizations should prepare for pricing changes and updated compliance requirements.   

Starting July 1, 2025: 

• Exchange Server licenses increase by 10% 

• Core CAL Suite increases by 15% 

• Enterprise CAL Suite increases by 20% 

Valid Software Assurance or Microsoft 365 licensing is required to stay compliant and eligible for updates. Hybrid-only servers remain free when configured via the Hybrid Configuration Wizard. 

Migration options: Cloud or on-prem 

IT teams have two clear paths forward, each with specific requirements and considerations. 

1. Migrate to Microsoft Exchange Online 

Recommended by Microsoft for long-term simplicity and flexibility: 

• Retire on-prem infrastructure 

• Access Microsoft 365 Copilot and cloud-only features 

• Eliminate manual patching 

Eligible organizations can access Microsoft FastTrack to support migration: 

• Step-by-step planning support 

• Templates, tools, and documentation 

• Direct engineer assistance for migration 

2. Stay on-premises with Exchange SE 

Required for organizations with: 

• Data sovereignty or compliance constraints 

• Legacy on-prem application dependencies 

• Hybrid directory integrations 

Upgrade path: 

• Exchange 2016 → Exchange 2019 CU15 → Exchange SE 

• Exchange 2019 CU15 → Exchange SE (in-place) 

Exchange Online vs. Exchange SE — Feature comparison 

Feature	Exchange SE (on-prem)	Exchange Online (cloud)
Infrastructure management	Customer-managed	Microsoft-managed
AI Features (Copilot, etc.)	Not available	Included
Security updates	Manual CU deployments	Auto-managed
What to do now: IT Action plan  With deadlines approaching, IT teams need a structured plan to ensure a smooth transition and avoid service disruption.  Use this step-by-step checklist to guide your next move:  Remove legacy versions Exchange 2013 or earlier Audit your environment  Run the Exchange Server Health Checker  Identify OS, schema, and CU levels  Upgrade client endpoints  Remove Outlook 2016 or 2019  Validate OAuth2 and MAPI support  Choose your strategy Compare Exchange Online vs SE for your business  Identify resource, timeline, and licensing implications  Check your licensing  Confirm SA status or Microsoft 365 coverage Engage your licensing partner for updates or renewals  Prepare your infrastructure Upgrade Exchange 2016 to 2019 CU15 if required  Validate Windows Server version compatibility  Test and validate  Rewrite PowerShell scripts for REST  Validate mailflow, journaling, signature tools  Communicate early  Inform stakeholders of end-of-life timelines, required steps, and downtime windows  Still using an Exclaimer on-premises solution?  Support for Exclaimer Signature Manager (Exchange or Outlook Edition), ended in September 2024. While the software may still run, there's no technical support if problems arise—including integration issues and SE compatibility.  We strongly recommend migrating to our cloud solution to maintain continuity and reduce risk.  Why move to Exclaimer's cloud solution:  Compatible with Exchange SE, Online, and hybrid  Supports server-side and client-side signature application  No on-prem infrastructure required  Web-based admin access  Automatic updates and enterprise-grade security 💡 Enterprise customer? Contact our Sales team for tailored migration assistance. Contact Sales Dave Willis Senior Content Manager Dave is a marketing expert with 15 years experience in the tech and SaaS world. He specializes in educating IT and channel audiences, with a focus on security, privacy, compliance, and marketing technology. With a talent for storytelling and a deep understanding of the industry, Dave transforms complex IT topics into clear, engaging, and impactful narratives. Book a demo See how Exclaimer helps you manage signatures across Exchange SE, Online, and hybrid environments—without the hassle. Book a demo Related articles Guides On-premises to cloud: A modern guide To email signature management Learn why organizations are moving from on-premises tools to cloud email signature management, and how cloud platforms improve control, scalability, and consistency. Read more Deeper Learning Revolutionizing email signature management: Make the switch from on-premises to the cloud Learn all about the benefits of migrating from on-premises email signature software to cloud-based email signature management. Read more Blog How Exclaimer delivers reliability and security at scale Learn how Exclaimer delivers reliable, secure email signature management—covering data handling, Azure hosting, certifications, and uptime. Read more Guides On-premises to cloud: A modern guide To email signature management Learn why organizations are moving from on-premises tools to cloud email signature management, and how cloud platforms improve control, scalability, and consistency. Read more Deeper Learning Revolutionizing email signature management: Make the switch from on-premises to the cloud Learn all about the benefits of migrating from on-premises email signature software to cloud-based email signature management. Read more Blog How Exclaimer delivers reliability and security at scale Learn how Exclaimer delivers reliable, secure email signature management—covering data handling, Azure hosting, certifications, and uptime. Read more