Microsoft Retires EWS API on Oct. 1; Third-Party Apps May Lose Email Access
On Oct. 1, 2026, Microsoft is discontinuing support for Exchange Web Services (EWS), a legacy connection technology used by some third-party email and calendar applications to access Microsoft 365 mailboxes.
EWS has been largely replaced by Microsoft Graph API and modern authentication methods. Retiring it will improve security, strengthen authentication protections, and allow Microsoft to focus development on current Microsoft 365 platforms.
Applications Impacted
As Microsoft continues to modernize authentication and messaging services, applications that depend on EWS will no longer be able to connect to CU Boulder's email services after Microsoft retires the technology.
Apple's Mail, Calendar & Contact Apps
Apple is actively working to update its native apps to use Microsoft Graph API, but those updates may not be available until after Oct. 1.
To provide users with time to transition to a supported Microsoft 365 application, or for Apple to release the necessary updates to its native apps, OIT is granting an exception that will allow Apple Mail, Calendar and Contacts to continue accessing CU Boulder email services until EWS is fully retired on April 1, 2027.
[Added 9/17, 3:36 p.m.] This extension will be granted automatically; users do not need to request it.
No extensions will be provided for other services.
Non-Apple Email Services
If you use a third-party email or calendar client that is not developed by Microsoft, we recommend proactively researching whether it supports Microsoft Graph API or is otherwise unaffected by the EWS retirement.
The following applications are known to either have not yet fully transitioned to Microsoft Graph API or to have done so only in the latest versions:
- Airmail
- BusyCal
- Canary Mail
- Cronofy
- EdisonMail
- eM Client
- Evolution-MUA-A
- Fantastical for Mac
- GNOME Evolution
- Mailbird
- SalesforceIQ
- Spark
- Thunderbird
- Thunderbird with Owl
This list may not include every affected application.
What You Should Do
If you currently use one of the affected applications:
- Identify whether your email client relies on Exchange Web Services (EWS).
- Begin transitioning to one of the Microsoft Outlook applications listed below.
- Verify that your email, calendar, contacts and any local data are synchronized before discontinuing use of your current application.
Recommended Email Applications
Microsoft's Outlook email applications use Microsoft's modern authentication and connectivity technologies and will continue to be fully supported.
Follow the links below to set up your CU Boulder email through Outlook:
- Outlook on the web
- Outlook for Mac
- Outlook for Windows
- Outlook for iOS (Microsoft Support)
- Outlook for Android (Microsoft Support)
Learn more about campus email and how to use Microsoft Outlook at CU Boulder.
Need Help?
If you need help migrating to Outlook or determining whether your email app is affected by this change, please contact the OIT Service Center at oithelp@colorado.edu or 303-735-4357.
