Microsoft Office 365 Calendar Integration
You can configure the IM and Presence Service to integrate with a hosted Office 365 server for Microsoft Outlook calendaring integration. When this feature is configured, the IM and Presence Service pulls user calender information from the Office 365-hosted Microsoft Outlook and displays it as a part of an IM and Presence user's presence status. If the user's Outlook indicates that the user is in a meeting that status displays in the user's presence status.
This integration has been tested successfully with 15,000 IM and Presence users system, where 5,000 users have a meeting at the top of the hour.