Exchange 2016 to Exchange Server SE Migration

Because Microsoft's in-place upgrade to SE exists only from Exchange 2019 CU14 or CU15 — SE is the 2019 code base with a new name and license, so 2019 can take it as if it were a cumulative update. Exchange 2016 is a different code base. From 2016 Microsoft's only supported route is the legacy upgrade: install SE servers into the same organization, coexist, move everything, uninstall 2016. That is what this service delivers.

Exchange Server Subscription Edition, released in July 2025, is functionally the same product as Exchange 2019 Cumulative Update 15 with later fixes and security updates; Microsoft's stated goal for the first release was to change nothing but the name, the license and the build number so that upgrades would be low-risk. The differences are commercial and lifecycle: SE is licensed as a subscription (or with active Software Assurance), it follows a modern lifecycle with continuous cumulative updates rather than a fixed end date, and it is the only on-premises Exchange that still receives security updates.

Three dates, all Microsoft's. Exchange 2016 support ended on 14 October 2025 per Microsoft's product lifecycle. Microsoft's paid Extended Security Update program for 2016 and 2019 has a second period covering May through October 2026, purchased separately, with nothing announced beyond it at the time of writing. And Microsoft has said that Exchange SE Cumulative Update 2 will block coexistence with 2016 and 2019 entirely — you must have removed 2016 before CU2 can be installed. CU1 has no published date as of Microsoft's August 2026 update, and CU2 follows it, so the honest answer is: sooner than is comfortable, on a date Microsoft will announce rather than negotiate.

Under Microsoft's terms, Exchange Server SE requires server licenses and CALs that are either subscription licenses or covered by active Software Assurance — or cloud subscription licenses such as Microsoft 365 E3 or E5 for every user and device that accesses the servers. A Standard CAL is always required; the Enterprise CAL is an add-on for specific features. Windows Server licensing for the new servers is separate. These are Microsoft's charges, not part of our fee; the target design states exactly what the environment needs, and our Volume Licensing practice can source it if you do not have a reseller.

Microsoft supports SE on Windows Server 2019, 2022 and 2025, and recommends the Server Core installation. We generally recommend Windows Server 2025 or 2022 for the longest support runway, chosen once: Microsoft does not support an in-place operating-system upgrade on a server that has Exchange installed, so the version you build on is the version that server runs until it is replaced. The design also sizes memory and storage to Microsoft's SE requirements, which are well above what a 2016 server needed.

Very little, if the namespace switch is done properly. Because SE proxies requests to mailboxes still on 2016, the client-facing names move to SE first and Outlook, mobile devices and Outlook on the web keep working without reconfiguration throughout coexistence. Each mailbox move is an online move: the user keeps working and gets a prompt to restart Outlook when the move completes. Downtime is confined to the short cutover windows for the namespace switch and mail flow, which we schedule with you.

A DAG cannot contain mixed Exchange versions, so the SE servers form a new DAG with its own databases, copies and witness, designed to your availability requirements rather than copied from the 2016 layout. Mailboxes move from the 2016 DAG's databases to the SE DAG's databases in batches. When the last mailbox is gone, the 2016 database copies and databases are removed, the servers leave the old DAG, and the DAG is deleted before the servers are uninstalled.

Exchange 2016 already uses modern public folders — they live in public folder mailboxes — so they move to SE the same way user mailboxes do, in the order the hierarchy requires, with item counts reconciled. If discovery finds public folder mailboxes at or beyond Microsoft's size limits or a structure that should be split, that remediation is scoped separately through our on-premises public folder migration service, and if you would rather retire public folders to Microsoft 365 that is an Exchange Online scope.

The hybrid moves with you. Once the SE servers are in and the namespaces point to them, we re-run the Hybrid Configuration Wizard from SE using Microsoft's dedicated Exchange hybrid app, move the migration endpoint and MRS proxy to SE, verify OAuth, organization relationships and free/busy in both directions, and confirm mailbox moves to and from Exchange Online still work. Microsoft blocked the legacy shared service principal for EWS in October 2025 and requires the dedicated app's Graph-based permission model by October 2026, so if your hybrid has not made that change yet, it happens here.

The public SAN certificate that covers your namespaces is normally re-used: exported from 2016 with its private key, imported and assigned on SE, and renewed on SE's schedule afterwards. The load balancer gets new pools and health probes for the SE servers, and one thing is checked early: SE enables Windows Extended Protection by default, which does not work with SSL offloading, so a load balancer configured to offload is switched to SSL bridging before the namespaces move.

Possibly, and we will tell you if so. Organizations with a regulatory, data-residency, air-gap or application reason to keep mailboxes on-premises are the audience for this page. If none of those apply, Exchange Online usually costs less per mailbox once the SE subscription, Windows Server, hardware, backup and patching are counted honestly, and it removes the next migration from your calendar. We scope the hybrid or cutover Exchange Online migration beside this one on the same call so the comparison is on real numbers.

$12 per mailbox plus a $4,950 base fee, as an estimate confirmed in a written quote before work begins — you pay after you approve delivery. A 500-mailbox organization with a two-server SE DAG comes to $10,950 on those figures. The base fee covers design, Active Directory preparation, the SE build, the namespace and mail-flow cutover and the 2016 decommission; the per-mailbox fee covers the batch moves and reconciliation. Estates above 2,000 mailboxes or with multi-site DAGs are quoted per estate. Microsoft licensing, Windows Server and hardware are separate and yours.

They are uninstalled through Exchange Setup, not powered off. Powering off leaves server objects, connectors and Autodiscover records in Active Directory that break hybrid wizards, confuse clients and haunt every future upgrade. The decommission moves the last system mailboxes, removes databases and DAG membership, transfers connector and address-book ownership to SE, uninstalls each server, and then verifies the directory is clean and that load balancer, DNS, monitoring and backup no longer reference the old names.

SE is a subscription product with continuous servicing: Microsoft ships security updates when needed and cumulative updates on its own cadence, and it supports only the most recent ones, so a server left alone for a year is both insecure and unsupported. The closeout hands you a patching runbook and the as-built documentation. Organizations that do not want to own that cadence can have us run it as a managed service, scoped separately from this migration.

Not directly. SE coexists only with Exchange 2016 CU23 and Exchange 2019 CU14 or CU15, so an organization on 2013 or earlier cannot install SE into it. The route is a two-hop plan — 2013 to 2016 or 2019 first, then to SE — or, far more often, a direct migration to Exchange Online, which has no such constraint. Tell us the version on the scoping call and we will lay out both.