you are composing in HTML. HTML makes extensive use of font sizes generically sized using a number from 1 to 7 that defines the size of the text. Browser default is 3. Given that you do not know the screen resolution of the recipients screen or the size of the device it is far more likely to product a good result is you stick to the basics of size larger and smaller. Like most folks, you appear to think point is a size is an absolute value that is portable. That is partially true, but in practice, not so much. You will find information suggesting it is 1/72 of an inch, but that is more a de facto standard but even so it does hold up fairly well. So if you set a font to 20 points, that is about 20/72 of an inch, or 7mm. On a 4 inch phone screen, that 7mm is fairly large, on a 26 inch desktop monitor is is somewhat insignificant. Add to the fact that the "normal" font of 3 is scaled to the size of the display and it's resolution, you may find you 20 point font is smaller than the "normal folder". Hence larger and smaller around that default size of 3. Size then becomes relative to the surrounding text. All of that to say, there is no real reason to use a point size in email unless you want your email to look unprofessional on some devices.