When attempting to use any kind of embed code in an HTML card in the editor, you'll see that this does not work as expected in a test email.
Since this is a limitation that is entirely controlled by external email clients, there is no way to make a dynamic embed work in an email. However, there is a workaround which some people use to share dynamic content in email newsletters:
- Take a screenshot of the embed
- Insert the screenshot as an image in the post
- Use the link feature to turn the image into a link, that opens your embed in a new tab
- Deliver the email newsletter to your members
- Once the post is published and delivered, you can optionally swap the screenshot for a real embed, which will be available for any visitors to that post on your website.
By default, Ghost automatically renders embeds for YouTube and Vimeo in your email newsletters so that readers are able to click on them and open the video as a link.