[bodyfour]

Do those IMAP servers allow separate control of the envelope recipients, or does it just take them directly from the message headers? To be fair, POP3's "XTND XMIT" had that flaw as well (IIRC qpopper just passed the message to "sendmail -t")

A proper mail submission command would preserve parity with SMTP by keeping envelope and headers distinct. I just want to leverage the fact that I've already auth'ed the user and shouldn't have to redo that to a separate server.

Also, presumably one of the advantages to the REST+JSON design of JMAP is to make it easy for javascript clients to use it. Since they can't do direct SMTP anyway there will presumably be some REST service that they will use for submission.

It just seems that it should be part of the same standard. Most mail readers are also mail senders.