Microsoft Exchange Web Services (EWS) Retirement - EOL - Jun 2026

Service Update

By	October 1st, 2026
Product(s)	Email Security - MX, Email Security Cloud Integrated Sync & Recover, Continuity for Office 365, Mimecast Synchronization Engine (MSE), Simply Migrate.
Who's affected	This change only affects customers using Mimecast with Exchange Online (Microsoft 365). If you use Mimecast exclusively with on-premises Exchange Server, no action is required. If you run a hybrid environment, read on to check which services may be affected.

Overview

Microsoft is permanently retiring Exchange Web Services (EWS) for Exchange Online. This is a Microsoft-driven, industry-wide change that affects every software vendor using EWS to connect to Microsoft 365. It does not affect On-Premises Exchange environments. 
Several Mimecast services currently depend on EWS and will be impacted from October 2026.

What's changing

Key dates 

• End of August 2026: Last chance to configure S&R AppID Allow list without service interruption.
• October 1st, 2026: EWS begins being disabled by default across Exchange Online tenants. Affected services will stop functioning for any tenant where EWS has been disabled. 
• April 1st, 2027: Full and permanent shutdown of EWS for Exchange Online. No exceptions and no re-enablement after this date. 

Services that will be discontinued 

These services will stop working when EWS is disabled for your tenant, either October 1, 2026, if Microsoft disables EWS automatically, or April 1, 2027, at the absolute latest. You will be notified before any service is discontinued.
 

Service	Status
Simply Migrate - Archive Mailbox	Will be permanently discontinued. No replacement planned
Mailbox Storage Management (MSE)	Will be permanently discontinued. No replacement planned
Managed Folders (MSE)	Will be permanently discontinued. No replacement planned
Mailbox Folder Replication (MSE)	Will be discontinued in current form. A new agentless, UI-based replacement is planned. Availability date to follow.
Calendar Replication (MSE)	Will be discontinued in current form. A new agentless, UI-based replacement is planned. Availability date to follow.
Sync & Recover - Restore (Cloud Gateway and Cloud Integrated)	Will be discontinued. Replacement may be available in the future if Microsoft addresses current Graph API parity gaps.

Services requiring migration required before October 2026

Individual migration guides will be published for each service, ahead of the recommended migration window. 

Service	Notes
Threat Remediation	A Graph API migration path is available. You should migrate to the new Graph API connector by following the instructions at Migrating Server Connectors. Additional benefits of switching include improved remediation speed and performance through a more secure connection.
Sync & Recover Cloud Gateway	A Graph API migration path is now available. Migrate your existing Cloud Connectors to use Graph permissions; existing EWS permissions will remain in place during the transition. For more instructions, see Sync & Recover - Migrating Connectors.
Continuity for Office 365 (Event Monitor)	New Graph API connector planned in the coming months. A migration guide will be provided.

Recommended actions

1. If you use Sync & Recover (Cloud Gateway or Cloud Integrated) Restore:

• To keep Restore fully functional through March 31, 2027, you must configure an AppID Allow List and set EWSEnabled=True in your Exchange Online tenant. Act before the end of August 2026; tenants that complete this before the deadline are excluded from Microsoft's automatic October 1st blocking. For more details, please refer to this Microsoft EWS migration guide

• If you miss the August deadline, you can still re-enable EWS after October 1st by setting EWSEnabled=True, but there will be a brief service interruption while the change takes effect. This option is available until April 1, 2027, after which EWS is permanently shut down with no exceptions.

2. If you use a service requiring migration (Threat Remediation, Sync & Recover Cloud Gateway, Continuity for Office 365):

• Threat Remediation: A Graph API connector is available. Migrate before October 2026 by following the instructions in Migrating Server Connectors.

• Sync & Recover Cloud Gateway: A Graph API migration path is now available. Migrate as soon as possible, and no later than October 2026. See Sync & Recover - Migrating Connectors for more information.

• Continuity for Office 365: No immediate action required. Individual migration guides will be published ahead of October 2026.

3. If you use a service that will be discontinued: No immediate action is required. You will be notified before any service is discontinued and when any planned replacements are available.

Full details are available in the EWS Retirement FAQ.

If you have any questions about this change, please contact your Mimecast Customer Success Manager (CSM), Account Executive, or Mimecast Support.

See Also...

• Microsoft Exchange Web Services (EWS) Retirement - Frequently Asked Questions
• Email Security - MX
• Continuity   
• Mimecast Synchronization Engine   
• Simply Migrate
• Sync & Recover
• Sync & Recover - Overview
• Threat Intelligence & Remediation
• Migrating Server Connectors
• Sync & Recover - Migrating Connectors

External links

• Microsoft Tech Community - Exchange Online EWS, Your Time Is Almost Up
• Microsoft Learn - Deprecation of Exchange Web Services in Exchange Online 
• Controlling access to EWS