JMAP: A modern, open email protocol

This environment has led to a stagnation in good email clients and limited innovation from email developers. It is a modern, efficient, easy-to-use API, built on many years of experience and field testing at FastMail, and refined with the collective expertise of many email developers at the IETF. We believe this free and open standard will help developers around the world work together to make email better for everyone.

Source: www.ietf.org