You can send a post as email by clicking on the caret (the arrow pointing down) next to Post and picking "Send as email".

From there, you can select your notification style, subject line and schedule it to be sent at a specific time.

If you choose to toggle on "ignore notification preferences", please note that this will override local settings and isn't recommend for regular communications. 

You can also edit the subject of your post and you can even create a dedicated channel for posts that you intend to send as email, to serve as a more interactive way to share announcements and other important community news.

Note that when you don't toggle "schedule send" and pick a specific date, the post will be published automatically.