Microsoft retires Exchange Web Services in Exchange Online

Microsoft has initiated the phased shutdown of Exchange Web Services (EWS) in Exchange Online, marking the beginning of the end for an API that has underpinned enterprise email integrations for nearly two decades. The move, announced years in advance, reflects Microsoft’s push toward its modern Graph API but leaves some organizations scrambling to identify and replace lingering dependencies before the final cutoff next year.

What is changing

Starting this week, Microsoft is flipping the default EwsEnabled setting from $null to $false for tenants in Exchange Online. This change blocks EWS access unless administrators explicitly override it by setting the value to $true and adding approved applications to an allowlist. Even with these temporary measures, EWS will be permanently disabled on April 1, 2027, with no exceptions. The retirement applies only to Exchange Online; on-premises Exchange Server installations remain unaffected.

EWS, introduced with Exchange Server 2007, has long served as the backbone for applications accessing mailbox data, including emails, calendars, and contacts. Microsoft deprecated the API in 2018, halting feature updates, and formally announced its retirement in 2023. Despite the years-long notice period, migration challenges persist, particularly for organizations with poorly documented or rapidly deployed integrations.

Migration hurdles

The primary obstacle for many organizations is identifying every system that still relies on EWS. Markus Müller, Global Field CTO for API management at Boomi, noted that incomplete documentation and ad-hoc integrations have left many teams unaware of their full dependency on the API. "With rapid integration rollouts and limited documentation, many lack a complete inventory of their EWS dependencies," he said.

"With rapid integration rollouts and limited documentation, many lack a complete inventory of their EWS dependencies." — Markus Müller, Global Field CTO for API management at Boomi, in The Register

Translation layers that convert EWS calls into Microsoft Graph requests can serve as a stopgap, but Müller warned they introduce additional maintenance overhead and do not eliminate the need for a full migration. Microsoft has not disclosed how many organizations or workflows still depend on EWS, but overlooked integrations will likely surface as tenants encounter unexpected disruptions in the coming months.

What to watch

Administrators who have not yet begun migrating should prioritize auditing their environments for EWS usage. Microsoft’s temporary allowlist provides a brief reprieve, but the April 2027 deadline is absolute. Organizations should also consider adopting API lifecycle monitoring practices to avoid similar surprises in the future, as Microsoft and other providers continue to phase out legacy interfaces in favor of modern alternatives.