Another related issue: nylas/nylas-mail#2873

I need this too! Looking forward to it. 13" 1080p (Fedora) display results in text a bit to small to read comfortably. In the mean time, I tried to change the config.json as directed here https://support.nylas.com/hc/en-us/articles/219130788-How-do-I-increase-the-font-size-in-Nylas-Mail- but it didn't work. Possibly because Nylas Mail seems to spawn new config files each time it is run, overwriting any changes made???

I suppose a custom theme with larger font sizes might fix the problem too... If this proves to be hard to do, maybe you could make a version of each included theme with +20%, +40%, -20%, -40% or whatever you think are options a number of people need.

@lamixer in the old issue Ben Gotow provided a theme with smaller fonts (because for me on 13" MacBook the problem is the opposite to yours), so probably you could take that as an inspiration to make a theme with bigger fonts.