We will be adding sending to the JMAP spec, although support may be optional. The way it currently works at FastMail is a bit too specific to our architecture though, so we want to clean it up before adding it to the spec.
>>> These proposals are always strongly opposed. It is one of the "attractive nuisances" of email protocols. The value of the capability is obvious to many people, but the high cost of having it in POP or IMAP is much less obvious.
