The HTML format, by now the standard for pretty much all email correspondence (business, marketing and even personal), allows for 2 ways of inserting images into messages – linking and embedding. The choice may seem trivial, but in reality the difference is between e.g. a marketing banner being displayed correctly in the recipients inbox or being blocked and displayed as the dreaded ’empty box with red x’ (Fig. 1).
Fig. 1. Famous ‘box with red x’ indicating issues with an image.