We have always used pixels, in line with w3c recommendations (e.g. http://www.w3schools.com/cssref/playit.asp?filename=playcss_font-size&preval=10px). The 'e' in 'email' stands for 'electronic'; why should standards based on the conventions of a paper-oriented industry apply here? Please explain to me how point sizes make sense if I view your email message on a) a smartphone with a small screen, and b) on a projector using a 2m wide screen? The important factor is making it comfortable and legible for the recipient; how you saw it when you composed it is almost entirely irrelevant. In my two examples here, we would reasonably expect the text size to be scaled suitably. Points are irrelevant. Points and other absolute sizes are fine if you're working with paper, where you have near-absolute control over paper size, font, size and face. Even then you can't guarantee that I will print it on the size of paper you had in mind (US letter vs A4 for instance) and that I have the ''exact'' fonts installed that you used. What paper size do you imagine an email gets printed on? Where is that defined? There is nowhere in email to set a paper size, nor absolute line lengths. Points are meaningless in such a situation. If you insist on imposing a specific font size on your hapless correspondents, I suggest you investigate the [https://addons.mozilla.org/en-US/thunderbird/addon/stationery/ Stationery] add-on where you can create and apply templates and set parameters such as size, face, justification, margins and more. But your correspondents are free to ignore or override your settings.