Microsoft Moves Cross-Tenant Calendar Sharing to Cross-Tenant Access Policies
Organizations using external Microsoft 365 collaboration features should begin migrating from legacy Exchange sharing configurations.
Key Takeaways:
- Cross-Tenant Access Policies will replace legacy Exchange-based sharing mechanisms.
- The change affects Free/Busy sharing, MailTips, and calendar sharing between Microsoft 365 organizations.
- Microsoft recommends testing and completing CTAP migrations before EWS retirement.
Microsoft is changing how organizations share Free/Busy availability, MailTips, and calendar data across different Microsoft 365 tenants. This change comes as Microsoft prepares to retire Exchange Web Services (EWS), which currently supports many of these cross-tenant collaboration capabilities.
Cross-Tenant Access Policy (CTAP) is a security and collaboration framework that enables organizations to control how users across different Microsoft 365 tenants interact. CTAP provides centralized, policy-driven controls for external collaboration, which allows administrators to securely manage access to resources such as calendar availability, shared calendars, MailTips, Teams, and other cross-tenant services.
EWS retirement drives changes to Microsoft 365 calendar sharing
Microsoft is making this change because the existing cross-tenant sharing features depend on Exchange Web Services (EWS), which is being retired. The transition to Cross-Tenant Access Policy provides a more modern, secure, and centrally managed way to support collaboration between Microsoft 365 organizations.
According to Microsoft, the Cross-Tenant Access Policy (CTAP) will become the new standard for sharing Free/Busy information, MailTips, and calendars between Microsoft 365 organizations. It replaces older Exchange Online mechanisms such as organization relationships, availability address spaces, and sharing policies.
This change mainly impacts companies that share calendar and availability data with external Microsoft 365 tenants, such as partners, subsidiaries, vendors, or acquired organizations. However, it doesn’t affect internal sharing within the same tenant.
The new Cross-Tenant Access Policy model is a part of Microsoft’s broader effort to modernize authentication and reduce reliance on high-privilege access methods. It should help to improve security and governance within enterprise environments.
What does the CTAP transition mean for IT admins?
Organizations that use Free/Busy sharing, MailTips, or calendar sharing with other Microsoft 365 tenants should review their current Exchange Online configurations and determine whether they rely on organization relationships, availability address spaces, or sharing policies. In this case, Microsoft recommends planning a migration to Cross-Tenant Access Policies to ensure these collaboration features continue to work after Exchange Web Services (EWS) is retired.
Additionally, organizations should test this new configuration before decommissioning their legacy settings and complete the transition as soon as possible. Moving to Cross-Tenant Access Policies provides a more secure and modern framework for collaborating with external partners, subsidiaries, and other Microsoft 365 tenants.
Rabia has a master's degree in Software Engineering and she has years of experience writing professionally about Microsoft products and other technologies. Rabia has also written for OnMSFT.com as well as Windows Report. She is always up to date on t...