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Exchange 2016 and 2019 End of Support: Exchange SE or Exchange Online?

Support for Exchange Server 2016 and 2019 ended on 14 October 2025. This guide covers the three migration paths, the decision criteria and a step-by-step migration checklist.

Published by: AnatoliaCore Technical Editorial Team

What Changed?

  • 14 October 2025: Microsoft support for Exchange Server 2016 and 2019 ended. After this date there are no standard security updates, bug fixes or technical support.
  • 1 July 2025: Exchange Server Subscription Edition (SE), the successor to on-premises Exchange, became generally available. SE uses subscription-based licensing and follows Microsoft's continuous support (Modern Lifecycle) model.
  • 1 October 2026: Exchange Web Services (EWS) in Exchange Online began to be blocked in stages, with full shutdown on 1 April 2027. This change affects Exchange Online only; EWS in on-premises Exchange continues.

What Does End of Support Mean in Practice?

The servers keep running; email does not suddenly stop one day. The real problem is invisible: no patch is released for a newly discovered vulnerability. Exchange is an internet-facing service through OWA and Autodiscover, and in the past it was compromised at many organizations through vulnerabilities such as ProxyLogon and ProxyShell. An unsupported Exchange server:

  • stays unprotected against new vulnerabilities,
  • is reported as an "outdated software" finding in KVKK and information security audits,
  • may run into compatibility problems with new operating system, browser and Outlook versions,
  • cannot get help from Microsoft support when something goes wrong.

Three Migration Paths

PathWhen does it fit?Points to watch
Exchange 2019 → Exchange Server SE (in-place)Data must stay on-premises; servers run Exchange 2019 CU14 or CU15Requires a subscription license; DAG members are upgraded one at a time
Exchange 2016 → Exchange Server SE (side-by-side)Data must stay on-premises; the current version is 2016Requires a new server, mailbox moves and proper removal of the old server
Full migration to Exchange OnlineYou do not want to manage servers and have no data location requirementApplication dependencies, EWS and SMTP sending must be resolved in advance
HybridA phased migration, or a need to keep some mailboxes on-premisesThe on-premises side must be kept on a supported version

Questions to Answer Before Deciding

  • Is there a contractual, sector or KVKK requirement for mail data to stay on-premises?
  • Is there a team to keep Exchange servers updated, monitored and backed up?
  • Does the budget favor a one-time investment or a monthly per-user subscription?
  • Which applications depend on email: scan-to-email from printers, ERP and CRM notifications, archiving and backup software?
  • What are the total mailbox size and archiving needs?
  • Will users also use other Microsoft 365 apps (Teams, SharePoint, OneDrive)?

If the answer to the last question is yes, Exchange Online is often the more natural choice; email comes as part of the Microsoft 365 subscription.

In-Place Upgrade from Exchange 2019 to Exchange Server SE

  1. Bring all Exchange 2019 servers to CU14 or CU15 and install the latest security update.
  2. Take a current backup of the databases and configuration, and verify that restore works.
  3. If you use a DAG, upgrade the servers one by one in maintenance mode; do not upgrade more than one member at a time.
  4. The SE installation works like a cumulative update; no Active Directory schema change is required.
  5. After the upgrade, check server health, certificates and security settings with Microsoft's Exchange Health Checker script.
  6. Update the SE licenses and product key.

Exchange Online Migration Checklist

  • Inventory: mailbox count and size, shared mailboxes, distribution groups, public folders.
  • Dependencies: printers and applications that use SMTP relay, integrations that use EWS, mobile device policies.
  • Identity: Will Active Directory users be synchronized with Entra Connect, or will cloud-only identities be used?
  • DNS: Lower TTL values a few days before the migration; plan the MX, Autodiscover, SPF, DKIM and DMARC records.
  • Method: cutover for a small number of mailboxes; hybrid with the Hybrid Configuration Wizard for a phased migration.
  • Pilot: test first with the IT team and a few volunteer users, then move in waves.
  • MX change: as the very last step, in a planned window.
  • Backup: set up an independent backup for Exchange Online mailboxes.
  • Old server: uninstall Exchange properly before shutting it down. In environments synchronized with Active Directory, the Exchange management tools are still needed for recipient management.

Common Mistakes

  • Shutting the server down and leaving it: servers shut down without uninstalling Exchange leave remnants in Active Directory and complicate later installations.
  • Forgetting scan and notification sending: after the MX change, printer and application emails stop silently.
  • Turning DMARC on straight at reject: legitimate but misconfigured senders are rejected too; monitoring mode should be used first.
  • Mistaking a retention policy for a backup: an independent backup must be planned separately in Exchange Online.
  • Overlooking applications that use EWS: in organizations moving to Exchange Online, these applications must be moved to Microsoft Graph.