Fix Zoho Calendar Free/Busy Lookups After Microsoft EWS Changes

From EWS to Microsoft Graph

Microsoft began blocking EWS requests on October 1, 2026, as part of a phased retirement that will culminate in a complete EWS shutdown on April 1, 2027. Azure applications that still depend on EWS permissions can no longer support Exchange Online availability lookups. Without an update, teams may lose visibility into Exchange Online users’ availability while scheduling events in Zoho Calendar.

Previously, Zoho Calendar used EWS-based permissions from your Azure application to retrieve Exchange Online free/busy information. These lookups now use the Microsoft Graph API, Microsoft’s strategic replacement for Exchange Online integrations. Your Zoho Calendar configuration stays the same. The existing Azure application needs the appropriate Microsoft Graph application permissions.

This change does not require a new system. It requires the permissions supporting the connection to stay current.

Organizations managing email migration or coordinating across Zoho services can also review how organizations migrate from Microsoft 365 to Zoho Mail. Administrators need to stay ahead of deprecation timelines across their workflows.

Who needs to act?

This update applies to organizations using:

• Zoho Calendar Interoperability with Exchange Online or Microsoft 365
• OAuth 2.0 authentication
• Azure application registrations that still use EWS permissions

Organizations using Exchange Server on-premises do not need to change their configuration for this transition. Zoho Calendar supports Basic Authentication for on-premises Exchange and OAuth 2.0 for Exchange Online.

To check your current configuration:

1. Sign in to Zoho Calendar using your primary domain.
2. Open Admin Console from the User profile section.
3. Select Interoperability from the left menu.
4. Choose Configure in the Exchange option.
5. Open Exchange Settings and review the authentication type configured for Exchange Online.

This check can help distinguish an EWS-related configuration issue from unrelated scheduling or authentication problems. Teams can also review how to troubleshoot invalid request issues in Zoho Mail by isolating the source of the problem.

Update the existing Azure application

Administrators should update the Azure application already used for Calendar Interoperability. In the Azure portal:

1. Add user availability permission: Add Microsoft Graph → Application permissions → Calendars.Read for user free/busy lookups.
2. Add room permissions if needed: If Include Rooms is enabled, add Calendars.ReadWrite, Place.Read.All, Schedule.Read.All, and User.Read.All.
3. Grant admin consent for the updated permissions.
4. Remove the old permission: Remove Office 365 Exchange Online → full_access_as_app.

Updating the permissions preserves the connection between Zoho Calendar and Exchange Online without creating a new application or rebuilding the interoperability configuration.

If your team needs guidance with Azure application updates or broader Zoho Calendar optimization, Creator Scripts offers expert consultation services for transitions like this.

What stays the same?

The transition does not require changes to these configuration elements:

• Application or client ID
• Client secret
• OAuth 2.0 token endpoint
• Exchange role account configuration
• Existing Zoho Calendar interoperability settings

You do not need a new Azure application. The change is limited to the API permissions used by the existing application.

Separate what is changing from what must remain stable. That helps administrators focus on the permissions that need attention and avoid unnecessary disruption.

You can get started with Zoho Calendar and explore its collaboration features with your existing Microsoft 365 environment.

Check room availability and credentials

User free/busy lookups require Calendars.Read. Organizations using Include Rooms must also add Calendars.ReadWrite, Place.Read.All, Schedule.Read.All, and User.Read.All.

Room scheduling is often where employees notice interoperability problems. Incomplete or inaccurate room availability can make a meeting harder to arrange, so include room permissions in your scheduling checks.

Organizations coordinating workflows across multiple systems may also use Zoho Flow to automate room booking confirmations, send notifications when availability changes, or connect calendar events with project management tools.

While updating the Azure application, verify that:

• The client secret is active and has not expired.
• Password expiration is disabled for the Exchange role account to help avoid service interruptions.
• Newly added rooms are included in a Microsoft 365 Rooms List.

An expired client secret, an expiring role-account password, or an unlisted room can disrupt an otherwise correct configuration. Teams managing several integrations can review Microsoft Office 365 integration patterns across the Zoho ecosystem.

Treat interoperability as ongoing work

The move from EWS to Microsoft Graph shows that integration depends on current APIs, well-managed permissions, active credentials, and clear ownership. The immediate task is to update the existing Azure application so Zoho Calendar can keep retrieving Exchange Online availability.

Leaders can use this change to ask which business processes depend on accurate free/busy information, who owns Azure application permissions, and how quickly the team can identify whether a problem comes from authentication, authorization, or API deprecation. They can also check whether room scheduling and user availability are treated as one employee experience, and whether other integrations rely on permissions approaching retirement.

Reliable availability sharing helps teams spend less time coordinating and more time making decisions. The technology may be invisible when it works, but its value becomes clear when a change threatens work.

Zoho Workplace provides an integrated suite of communication and productivity tools, including calendar, mail, meetings, and document collaboration, designed to work together and reduce dependency on multiple vendor integrations.

For help with Azure application updates, Zoho Calendar optimization, or Microsoft 365 interoperability planning, Creator Scripts provides consultation and implementation services. You can contact Creator Scripts, explore Zoho Integration Services, or visit the Creator Scripts Support Portal. For more Zoho Calendar insights and platform updates, visit the Creator Scripts Blog.