That seems to be the case for my app. It was sending an HTML email with the appspot domain used for the logo: https://example.appspot.com/images/logo.png https

That seems to be the case for my app. It was sending an HTML email with the appspot domain used for the logo: https://example.appspot.com/images/logo.png https://example.appspot.com/images/logo.png Changing that to http://www.example.com/images/logo.png http://www.example.com/images/logo.png fixed the problem, but now I have to host the image elsewhere on a HTTPS enabled domain. A separate question is what has google done with all the messages that users of this app sent? Are they gone for good, or stuck in a queue somewhere?