Short answer
Exchange Server 2016 and 2019 reached end of support on October 14, 2025, so they no longer receive security updates. Your main options are moving mailboxes to Exchange Online, upgrading to Exchange Server Subscription Edition (SE), or running a hybrid that keeps a small supported on-premises footprint. Staying on the old versions leaves an internet-facing server unpatched.
Key facts
- Exchange Server 2016 and 2019 reached end of support on October 14, 2025.
- Exchange Server SE is the supported on-premises successor and needs subscription licensing.
- Exchange 2019 on a current cumulative update can upgrade in place to Exchange SE; Exchange 2016 cannot.
- Hybrid organizations that sync with Entra Connect still need a supported way to manage recipients.
- An inventory of apps and devices that relay mail is required before any server is retired.
What end of support means in practice
End of support does not switch Exchange off. Mail keeps flowing. What stops is security updates, bug fixes and Microsoft support. Exchange servers are exposed to the internet for mail flow, Outlook on the web and Autodiscover, which makes an unpatched server a high-risk target.
Cyber insurers, auditors and compliance frameworks increasingly ask whether mail systems are supported. Running an unsupported version can make those conversations harder even if nothing has gone wrong yet.
Option 1: Move to Exchange Online
For most SMB and mid-market organizations, moving mailboxes to Exchange Online is the simplest long-term answer. Microsoft patches the service, and features such as Defender for Office 365, Purview retention and Copilot work best with cloud mailboxes.
The migration path is usually Exchange hybrid with remote move batches, or a cutover for very small organizations without directory sync. Public folders, shared mailboxes, room mailboxes and mail-enabled apps all need to be in the plan.
Option 2: Upgrade to Exchange Server Subscription Edition
Exchange Server SE is the supported on-premises version. It fits organizations with regulatory, data residency or network reasons to keep mailboxes on their own servers. It requires subscription licensing for servers and users, through Software Assurance or a cloud subscription that includes the rights.
Exchange 2019 servers on a recent cumulative update can be upgraded in place to SE. Exchange 2016 cannot, so those environments need new SE servers and mailbox moves, which is effectively a legacy on-premises migration. Plan hardware or virtual machines, a supported Windows Server version, certificates and load balancing.
Option 3: Hybrid with a minimal on-premises footprint
Many organizations moved mailboxes to the cloud years ago but kept an Exchange server for hybrid and recipient management because they sync identities with Entra Connect. That remaining server also reached end of support if it runs 2016 or 2019.
There are two common paths. Upgrade the hybrid server to Exchange SE so it stays supported, or remove the last Exchange server and manage recipients with the Exchange Management Tools and PowerShell, which Microsoft supports for fully migrated environments. Removal needs care: SMTP relay, hybrid free/busy and any remaining on-premises mailboxes must be handled first.
Comparing the options
| Option | Best fit | Main work |
|---|---|---|
| Exchange Online | Most SMB and mid-market organizations | Hybrid or cutover migration, relay redesign, decommission |
| Exchange SE in place | Exchange 2019 shops that must stay on-premises | Update to a current CU, SE licensing, upgrade and test |
| Exchange SE new build | Exchange 2016 shops that must stay on-premises | New servers, mailbox moves, retire 2016 |
| Hybrid, upgrade last server | Cloud mailboxes with directory sync and ongoing hybrid needs | Upgrade hybrid server to SE, keep connectors current |
| Hybrid, remove last server | All mailboxes in cloud, relay already moved | Move relay, switch to management tools, decommission |
Before you pick: inventory mail relay
Whichever option you choose, the most common outage cause is forgotten mail relay. Scanners, ERP systems, monitoring tools, building systems and scripts often send mail through Exchange by IP address. Review receive connector logs and message tracking to find every sender, then point each one to Exchange Online connectors, SMTP AUTH where still allowed, a relay service, or a supported on-premises relay before any server is retired.
How Accred Consulting approaches it
Accred Consulting begins with discovery of your Exchange version, mailbox count, hybrid state, directory sync and every app or device that relays mail. The Proposal recommends one path, with a clear scope, fixed price and timeline. In one Exchange Server exit, the relay inventory prevented an outage. For an approximately 460-mailbox hybrid client, free/busy was moved from EWS to Microsoft Graph in 4 weeks. US-based specialists run delivery with structured check-ins, and handover covers documentation and knowledge transfer for whatever stays on-premises.
Track record: 400+ client projects, 2,000+ migration workstreams and 150,000+ users migrated by a US-based team. Company facts · Case studies
Related questions
Want this scoped for your environment?
Book a free consultation. After discovery you get a written plan with scope, a fixed price and a timeline.
Book a free consultation