Exchange Web Services Retirement: Action Plan for Admins

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Allow List Setup, Cross-Tenant Migration, and Graph API Cutover

The Exchange Web Services retirement enforcement phase begins October 1, 2026, leading to a permanent shutdown on April 1, 2027.

Microsoft introduced EWSAllowedAppIDs to let administrators build an explicit allow list of approved applications before Exchange Web Services (EWS) enforcement starts. Setting EWSEnabled to $true activates this policy enforcement. Consequently, only registered Application IDs retain access, while unlisted integrations receive an HTTP 403 error. Furthermore, legacy cross-tenant Free/Busy, MailTips, and Calendar Sharing rely on the Microsoft 365 Cross-Tenant Access Policy moving forward.

Core Milestones and System Configuration Rules

To help manage your cutover from EWS to Microsoft Graph, keep these timeline rules in mind:

  • App ID enforcement: Only applications explicitly registered in EWSAllowedAppIDs maintain connectivity after October 1, 2026.
  • Cross-tenant migration: Cross-tenant Free/Busy and Calendar Sharing shift to Cross-Tenant Access Policies between September and October 2026.
  • Scope boundaries: The Exchange Web Services retirement applies exclusively to Exchange Online; hybrid on-premises mailboxes fall outside this scope.

Action Plan for Exchange Online Administrators

Because unlisted applications will face access blocks, administrators should execute three critical steps:

  • Audit EWS usage: Pull tenant EWS usage reports to build an inventory of dependent scripts and third-party integrations.
  • Configure allow lists: Register necessary Application IDs within EWSAllowedAppIDs to prevent service disruptions.
  • Rebuild cross-tenant sharing: Transition organization relationships to Microsoft 365 Cross-Tenant Access Policies.

How our team helps you prepare:

  • EWS Application Auditing: We identify hidden scripts, line-of-business apps, and third-party tools relying on legacy EWS calls.
  • Microsoft Graph Migration: We refactor custom EWS code and rebuild integrations using modern Microsoft Graph endpoints.
  • Cross-Tenant Policy Configuration: We configure Cross-Tenant Access Policies to keep cross-tenant sharing working uninterrupted.

Need help verifying your legacy integrations before enforcement begins? We can help audit your environment and map your migration to Microsoft Graph.

Graphic with text: Exchange Web Services Retirement: What Admins Do Now. Simple SharePoint, a division of Rego Consulting.

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