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 | Administrators |
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
- 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 being permanently discontinued
(no direct replacement available after October 2026 / April 2027, depending on when EWS is disabled for your Microsoft tenant)
| Service | Status |
| Mailbox Storage Management (MSE) | Permanently discontinued. No replacement available. |
| Managed Folders (MSE) | Permanently discontinued. No replacement available. |
| Simply Migrate - Archive Mailbox | Permanently discontinued. No replacement available. |
Services temporarily paused (not permanently discontinued)
| Service | Status |
| Sync & Recover - Restore function (Email Security - MX and Cloud Integrated) | Temporarily unavailable. Sync and all data retention unaffected. PST/EML export available as interim workaround. |
| Simply Migrate - Legal Hold (Recovery Hold) | Temporarily paused pending Microsoft's replacement API reaching general availability. |
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 | Graph API migration path available. Migration guide to follow. |
| Sync & Recover - Sync (Email Security - MX) | New Graph API connector planned for release between April and May 2026. Migration guide will be provided. |
| Continuity for Office 365 (Event Monitor) | New Graph API-based connector required. Setup guide will be provided. |
| Mailbox Folder Replication (MSE) | Being rebuilt as a new agentless, UI-based solution. Availability date to follow. |
| Calendar Replication (MSE) | Being rebuilt as a new agentless, UI-based solution. Availability date to follow. |
Recommended actions
-
If you use a discontinued service (Mailbox Storage Management, Managed Folders, Simply Migrate Archive Mailbox):
Export any data you need to retain before September 2026. Do not rely on the April 2027 hard deadline. Microsoft's phased disablement begins in October 2026 and the timing for individual tenants is outside Mimecast's control. Detailed export guidance will be published ahead of the deadline. -
If you use a paused service (Sync & Recover Restore, Simply Migrate Legal Hold):
No action required at this time. Mimecast will notify you directly when these features are re-enabled. -
If you use a migration-required service:
No immediate action required. Watch for individual product communications with step-by-step migration guides. Threat Remediation customers can begin migration now. The migration to new connectors has a deadline of October 2026,
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
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