Scheduling Mail

With the Apple mail client, alone? Not easily.

Automator can likely be used here, triggering the send off a calendar event.

It’s going to be clumsy, though.

There’s at least one available plug-in for this that can be easier, though.

https://www.mailbutler.io/apple-mail

And Outlook client can provide this, as can some mail providers.

We aren’t folks that work for Apple, we’re other users. Why Apple does or does not provide some feature?

Here’s how to let the folks that work for Apple know about your request: Product Feedback - Apple

Load Outlook or another mail client, or use a mail service, or a mail manager, or other existing means of managing mail.

I’ve had approximately no need for this when using (non-automated) mail, that going back as far back as the 1980s.

And I’ve realized mail is a tacho for managing information and contacts. Wonderful way to hide info, though.