Depends on your requirements but, JMAP ( JSON Mail Access Protocol (jmap) ) is on its way. [1] https://www.ietf.org/blog/jmap/ https://www.ietf.org/blog/jmap/

Depends on your requirements but, JMAP ( JSON Mail Access Protocol (jmap) ) is on its way. [1] https://www.ietf.org/blog/jmap/ https://www.ietf.org/blog/jmap/ [2] https://datatracker.ietf.org/wg/jmap/about/ https://datatracker.ietf.org/wg/jmap/about/