Updated: October 23, 2023 (October 23, 2023)

Which APIs for Which Exchange?

As managing vice president, Rob Helm covers Microsoft collaboration and content management. His 25-plus years of experience analyzing Microsoft’s technology... more

Oct. 20, 2023: Exchange Online will block Exchange Web Services (EWS) from all client applications other than Microsoft’s starting Oct. 1, 2026. See: “Exchange Online Blocks EWS in Oct. 2026”.

Applications for Exchange Server and Exchange Online management and compliance will use both Exchange Web Services and Microsoft Graph APIs for the foreseeable future.
Developers must choose between the APIs based on mailbox hosting, features, and long-term prospects.

Exchange Online and Exchange Server API roadmaps changed in Mar. 2022. The changes affect which API developers should use in third-party and custom applications for Exchange migration, backup, eDiscovery, and other tasks. As shown in the accompanying diagram, the changes affect two APIs: Exchange Web Services (EWS) and Microsoft Graph.

EWS Survives On-Premises and for Some Features Online

EWS is a legacy API used by applications to remotely access Exchange Server and Exchange Online data.

EWS remains the API for access to on-premises mailboxes in Exchange Server. For Exchange Online, Microsoft has been encouraging developers to use Microsoft Graph instead. It plans to shut down some EWS features for Exchange Online on Mar. 31, 2022, and it has been replacing EWS in its own Outlook clients.

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