Way to go! At Cozy cloud(https://www.cozycloud.cc/) we are developing an open source personal cloud platform that you can self-host and assign your own domain.
Right now we already offer backup of your email address but we would like to offer a good web-mail alternative.
Have you got suggestion for a Node.js mail client we could cook in?
(Of course I have to keep a backup of all the mail, but that's as easy as having some client download it.)