I've used the code from EmailOnAcid for implementing HTML5 video into e-mails, and it works in all clients,except for the standard mail client in iOS11. https://www.emailonacid.com/blog/article/email-development/a_how_to_guide_to_embedding_html5_video_in_email The thumbnail of the video is shown, but it just keeps buffering, and never plays. The only way to get iOS11 to play the video, is by closing the e-mail app, and reopening it. Then it can play the video.
Is there a solution for this, or at least some CSS to target iOS11 to make a fallback?