When I include a Spotify song embed in my post via the supported Spotify editor utility, the embedded song card (player and link) is viewable in the browser and mobile, but disappears in the email newsletter. Note that the song card is viewable in the newsletter preview.
I would expect the song card to be visible in the email, even if its not interactive/functional.
Steps to Reproduce
Create a post in the official “Edge” theme
Add an embedded song link via Spotify.
Preview the post to see that it shows the song card.
Send yourself a test email and notice that the card is absent.
I’m just a volunteer mod, but I’ll offer my feedback:
There a lot of different kinds of embedded content, and I think it would be hard to make solution that works for all the cases. Taking a “screenshot” to make a PNG is not easy either. The libraries I’ve dealt with are complex and can be fragile and not one I would b eager to add as a dependency.
I agree it would be nice if Ghost removed iframes from email previews (and emails) if they aren’t going to render in most email clients.
When in doubt, use the feature to send yourself a test email and see how it looks.