JMAP is a new protocol designed to streamline network resources and simplify development for email users. The protocol is stateless, without a persistent connection, making it ideal for mobile connections with intermittent network access. The flexible set of commands enables single JMAP operations to be batched together, while backreferences make it easy to detect and sync changes. JMAP also offers flood control, allowing clients to set limits, and makes it easy to throw away cached data and refetch. While binary data is not transported in JSON, it can upload/download attachments separately through HTTPS.
https://jmap.io/