What is required to achieve free/busy interoperability between Google and Microsoft Exchange?

To achieve free/busy interoperability between Google and Microsoft Exchange, it is essential to ensure that Exchange web services are accessible over a secure connection. Opening these services on port 443 allows for the secure transmission of data using HTTPS. This is critical because Google Calendar needs a secure method to communicate with Microsoft Exchange's calendar services in order to access and share free/busy information. By using HTTPS, the data exchanged is encrypted, providing both security and integrity during the communication process.

The requirement for secure access highlights the importance of protecting sensitive calendar data while ensuring interoperability between two different systems. This setup allows users on either platform to see free/busy status, enabling effective scheduling of meetings and resource management across Google and Microsoft environments.