Major email clients including AOL, Gmail, Yahoo, and Outlook don’t support embedded videos, so your recipients will either not be able to watch your video within the email, get delivered to SPAM or just get rejected because of size.
However, there are 2 ways round this
1. Use a Simple Image
The best way to do video in emails is to create an image that looks like a video player that the reader can click, something like this, with the big ‘Play’ button in the centre:
It has the appearance of an embedded video player but is actually just an image with a link added – when they try to click the Play button in the centre, they click the link which takes them to where they can view the video.
2. Use an Animated Gif
Go to Imgflip.com, a tool that enables you to create GIFs of videos. You can upload a URL directly to Imgflip, or you can upload a video you have saved on your computer. It will create an animated gif for you to embed in your email. Be aware that not all email clients play animated gifs automatically.
Here are 2 really good articles on the subject