Embeddable extensions of the functionality of email and calendaring applications are described herein. An originating email and calendaring application formats meeting items to include extensible content, e.g., within the body field of the meeting item. Recipient email and calendaring applications receive the meeting items and, depending on whether they are configured to provide an extended functionality, will either deploy the extensible content item according to the extended functionality or present the extensible content item according to a standardized functionality. The body field includes the extensible content item according to the standardized functionality that is interpretable by configured clients to provide the extended functionality.