Email clients will not typically not display scripted elements or embedded videos (exception: Apple mail on the Mac, which may play embedded HTML 5 videos using the <video> tag).
For now you basically have to give up on video working in email. Instead, have an email service that converts the embedded video to a thumbnail automatically, or at least offer an alternative link for email readers to use in your post so they can click through to view. You can't really avoid having email readers clicking through to something to watch your video; whether it's your post or your YouTube channel is a decision you can make if you add the alternate link yourself.