Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
have you even looked at k9 mails setting options? because it can make the text pretty big (if you still cant see it on the largest i am sorry and will continue looking for you) but open up k9 mail then it menu- settings- display- font size and then just navigate to what you want to make larger if you want the body of the messages larger click messages then message body. hope that helps