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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
“Exchange Server SE isn't the next version, it's a shift in how the platform is maintained. It moves to Microsoft's modern lifecycle model: no more fixed end-of-life dates. You get two cumulative updates a year, and staying supported means keeping pace, on either the latest update or the one behind.”
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.
Our Legacy Signature Manager solutions aren’t supported by Exchange SE, and compatibility can’t be guaranteed. To restore support and access enhanced email signature management features, we recommend migrating to our cloud solution now.
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.
“Once the first cumulative update ships, the differences start to matter: NTLM replaced with Kerberos for back-end authentication, a REST-based admin API beginning to replace remote PowerShell, and Outlook Anywhere deprecated. Most importantly, coexistence with Exchange 2016 and 2013 will be blocked, so the gradual migration that worked in the past won't work.”
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.
Key takeaway
Only four months exist between SE's release and Exchange 2016’s support end. Migrate to Exchange 2019 now to stay eligible for in-place upgrades.
Technical deprecations in Exchange SE
Starting with CU1 (expected late 2025), Exchange SE will enforce modern protocols:
Deprecated/Removed | Replacement/Action |
|---|---|
Remote PowerShell (RPS) | REST-based Admin API |
Outlook Anywhere (RPC/HTTP) | MAPI over HTTP |
NTLM authentication | Kerberos (Negotiate:Kerberos) |
Coexistence with 2016/2019 | Decommission before CU1 installs |
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.
Key takeaway
Once CU1 is installed, coexistence with Exchange 2016 or 2019 is no longer supported.
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.
“You can't buy Exchange SE outright. Every user accessing the server needs active Software Assurance or a qualifying Microsoft 365 subscription, including hybrid setups. The old free hybrid licence is gone, so every hybrid mail flow now requires a paid entitlement per user.”
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
“Moving fully to the cloud reduces your attack surface. Hybrid needs more public exposure by definition, connectors, endpoints, and credentials across two systems. A cloud-native setup centralizes authentication through something like Entra ID, retires legacy protocols, and applies conditional access. The risk isn't where the infrastructure sits, it's how it's configured and how many dependencies it drags behind.”
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)
Tip
Remove Exchange 2013 or earlier before upgrading.
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
“A modern lifecycle means no ten-year support timeline. Exchange SE stays supported as long as you stay current: cumulative updates twice a year, no skipping versions, no set-and-forget. The upside is that if you keep pace you're always supported with an infinite horizon instead of a countdown to the next big migration.”
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.
