I had the same problem with the mail app for ages. Incoming mail was illegible. I had set the font sizes to max with no effect. I was going to give up and leave Protonmail. Then I tried signing in using the browser window and emails coming in this way were fine and perfectly readable.
I had the same problem with the mail app for ages. Incoming mail was illegible. I had set the font sizes to max with no effect. I was going to give up and leave Protonmail. Then I tried signing in using the browser window and emails coming in this way were fine and perfectly readable.