iOS Users Unable to Sign In to Mimecast Mobile - Jun 2026

Updated

Known Issue

Date Logged June 24th, 2026
Product(s) Mimecast Mobile - iOS
Status Not Fixing

Issue

We have identified a Single Sign On (SSO) failure on devices enrolled in Microsoft Intune after August 2025, where users are unable to sign in to the Mimecast Mobile App for iOS.
This is due to a compatibility issue between the app's authentication method and Microsoft's updated device identity model.

From August 2025, Microsoft moved device identity key storage to Apple's Secure Enclave for all newly-enrolled iOS devices. For SSO to work under this model, apps must authenticate via Apple's system authentication session, which allows the SSO Extension to intercept the request and pass device identity to the identity provider. The Mimecast Mobile app uses an embedded browser for authentication which is sandboxed and cannot interact with the SSO Extension, or pass device identity to Microsoft Entra ID. As a result, the authentication flow does not complete. This is an architectural limitation of the app and cannot be resolved via configuration on either the Mimecast or customer side. Devices enrolled before August 2025 are not affected.

Symptoms

  • The Mimecast Mobile App for iOS fails to complete the SSO login process on devices newly-enrolled in Microsoft Intune since August 2025. 
  • Users are presented with a sign-in screen that does not progress.
  • The app receives a valid SAML challenge from the server, but never opens a browser session to the identity provider. 
  • Users are left on a loading spinner with no way to authenticate. Devices enrolled before August 2025 are not affected.

Workaround

There is no configuration-based fix available. We recommend transitioning affected users to one of the following alternatives, both of which authenticate via the system browser and are fully compatible with the Microsoft Enterprise SSO Extension, device compliance, and Conditional Access policies: 

  • Mimecast Personal Portal: Available via Safari or any managed browser on iOS. 
    No installation is required, and no changes to Conditional Access, or Intune policies are needed. See Mimecast Personal Portal - Overview.
  • Mimecast User Portal: Our next-generation Progressive Web App (PWA), installable on iOS home screens for an app-like experience. Fully compatible with modern MDM and Conditional Access requirements. See User Portal - Overview.

See Also…

 

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