Email design is really tricky when it comes to responsive stuff. This article shows some problems with the existing practices of really popular brands and goes through how to make them more accessible.
This view was not unique to my situation, nor caused by a bad internet connection. For about 50% of the recipients, images do not show by default. Either because they choose not to waste data before determining something is of interest, or because their email clients likes it that way.An excerpt from Convert a static email to a responsive design