Users with a Microsoft personal account may encounter the following error when trying to create a Teams online meeting in eM Client: “Default calendar is not known”.

In the Online Meeting logs this typically appears as:

• "AuthenticationError – Error authenticating with resource"
• "allowedOnlineMeetingProviders":["unknown"]
• "defaultOnlineMeetingProvider":"unknown"

This issue started after Microsoft retired Skype in May 2025 and moved users to Teams Free. Personal Skype users could sign in and keep their chats and contacts, and Teams initially worked in eM Client.

As the migration progresses, MS personal account users now report being unable to create new online meetings and see the error above.

This is caused by how Microsoft permits online meeting creation:

• eM Client (a third‑party app) must use the Microsoft Graph API to create online meetings.
• Microsoft’s Graph API restricts Teams meeting creation to Microsoft 365 work or school (Azure AD) accounts with Teams enabled and licensed.
• Personal Microsoft accounts are not supported for this API, so the request is blocked and eM Client shows “unknown” as the provider. This is why Teams works in Outlook or the Teams app (which use Microsoft’s internal APIs) but not through eM Client.

Solution:

If you need to create Teams online meetings in eM Client, you must use a Microsoft 365 work or school account that has Teams properly enabled and licensed.

Personal Microsoft accounts cannot be used to create Teams meetings via eM Client (or any third‑party application) because the Graph API does not support this scenario.