Exchange Server 2019

Exchange Server 2019 has two editions: Standard, which supports up to five mailbox databases per server, and Enterprise, which raises the cap to 100. Both editions ship the same feature set otherwise — Database Availability Groups (DAGs), client access services, transport rules, anti-malware, and the on-premises management console. Enterprise is the right choice for most production deployments because the five-database cap on Standard is hit quickly once mailbox sizes and tiering policies are factored in. Pricing is per-server.

Every user or device with a mailbox or that uses Exchange features needs a Client Access Licence. Standard CALs cover core email functionality. Enterprise CALs are additive to Standard CALs (you need both for any user that uses Enterprise CAL features) and unlock unified messaging, advanced compliance (in-place hold, in-place eDiscovery, Data Loss Prevention), and per-user journaling. Most production deployments on Exchange 2019 carry Standard CALs for the bulk of users and Enterprise CAL add-ons for executives and regulated roles. Service accounts and conference-room mailboxes also count unless explicitly excluded by service-account exception terms.

Extended support for Exchange Server 2019 runs through 14 October 2025 with security updates only — no new cumulative updates after CU14, no feature work, no design changes. Exchange Server Subscription Edition (SE) shipped in mid-2025 and is the supported on-premises continuation: it is technically equivalent to a refreshed 2019 with a subscription licensing model layered on top. In-place upgrade from 2019 CU14 to SE is supported and is the recommended path for estates that want to keep mail on-prem. For estates that want to retire on-prem Exchange entirely, the cutover migration to Exchange Online (as part of Microsoft 365 or Office 365) is the alternative path and the one most organisations are choosing.

Hybrid Exchange — a configuration where Exchange Online and Exchange Server share an SMTP domain, address book and free/busy lookups — is the staple migration tool. The Hybrid Configuration Wizard automates the trust setup, certificate provisioning and connector configuration. Mailbox moves are non-disruptive to end users: Outlook reconfigures itself, OWA redirects transparently. Once all mailboxes are in Exchange Online, the on-prem Exchange organisation can be decommissioned, with the historical caveat that until 2024 a single on-prem Exchange Management server was still required for Entra ID Connect attribute writeback — a requirement Microsoft has now lifted via the Exchange Modern Hybrid configuration with cloud-based management tools.

Running Exchange 2019 in extended support means receiving security-only updates through October 2025 (already past for most cohorts) — no protocol additions, no Office 365 connector compatibility work, no fixes for cosmetic or performance issues. Security advisories continue to be issued and patches continue to ship for vulnerabilities rated Critical, but anything else is on the customer to mitigate or wait out. For organisations that have not started a migration, the realistic options at this point are: bite the bullet and migrate to Exchange Online, in-place upgrade to Exchange Server SE and adopt the subscription model on-prem, or accept the documented risk of running an unpatched mail server.