Scheduled / delayed sending is not documented?

Scheduled sending has otherwise been a luxury only available to non-standard implementations with custom interfaces, such as GMail, or Novell Groupwise (if I recall correctly). For me, the usecase for such a feature is this:

• Marketing, events-related, or personal outreach emails typically have a context/timing-sensitive aspect, so I'd like to be able to schedule them (especially considering the timezone of the person I'm contacting). It also helps productivity tremendously to be able to schedule communications in advance.
• Humanistic, respectful staff managers and directors know that it is better to schedule mails to staffers to their business hours, avoiding emails that would arrive outside work hours and cause undue stress or cognitive load. Basically, mindfulness for staffers' "right to disconnect".

It seems to me that a key selling point for JMAP could be a standardized way to "schedule send" individual emails, server side via the email client, without resorting to silly client-side hacks like what we've been seeing in the POP+IMAP world. As part of this, the intended UX would also include the ability to edit the scheduled time or cancel the sending, reverting it to a draft, or editing the email's contents before it is sent (all things that I can do with GMail's web UI, which is one of the reasons I'm stuck with GMail).

Surely you must have thought of this, but so far I'm unsure to which extent; I Ctrl+F'ed for "schedul" or "delay" in:

• JMAP Client Guide
• JMAP Server Implementation Guide
• JMAP Specifications
  • JMAP Mail Specification

...and only found a single mention, in the "Mail Specification" page, a maxDelayedSend variable. There does not seem to be other similarly-named variables or explanations with the two keywords I used.

So is this part of the spec from the start, and if yes, is it just not well documented? Otherwise, shouldn't it be part of it?

This would probably make for a more compelling protocol pitch to email clients (like Evolution) if you could say "...and you get clean, standardized scheduled sending in Evolution (or Cypht) for free! The docs about that feature are there..."

Start with the JMAP Mail Specification's maxDelayedSend mention, then compare the JMAP Client Guide, Server Implementation Guide, and Specifications pages for scheduled or delayed sending. Determine whether the existing behavior is fully specified or whether a new protocol feature is being proposed; document the relevant behavior or define the scope of a specification change.