I was told to come here and post about this particular font. I don't know if it can be added to the Fastmail interface, or if we can be allowed to choose our own. I have some macular degeneration now in my oldish eyes
and here's how I can read for hours with no eyestrain:
1. Dark grey background with light grey text (white text is too bright)
2. Martel font. --- I've found this font extremely easy on the eyes and easy to read, especially if you can enlargen it.
I read reddit for hours and have changed everything I can to Martel now because it looks so good and is so readable.
My two cents. Thanks!