Nope, that needs to be solved in SMTP. Unfortunately, JMAP only replaces IMAP/POP. I have personally been working on a new protocol that replaces both IMAP an

Nope, that needs to be solved in SMTP. Unfortunately, JMAP only replaces IMAP/POP. I have personally been working on a new protocol that replaces both IMAP and SMTP. It's not ready yet, but the solution turns out to be quite elegant and I have great hope that it will work in the future.