> That says the submit server's IMAP client must support STARTTLS+SASL > PLAIN authentication.
Yes. > Which is exactly the opposite of what X-PLAIN-SUBMIT does. X-PLAIN-SUBMIT is intended to allow a submission server to connect to the IMAP server, send STARTTLS, and then authenticate using a plain-text password -- even when PLAIN is disabled for normal users. Nothing more. We just didn't want URLAUTH to break when the administrator shuts down PLAIN auth.
