A decent number of my incoming emails are very difficult to read. The font is extremely small. By the way: all other apps for mobile phones I know have this difficulty as well.
From my perspective, these are the causes:
the email contains a (relatively large) image that is not attached but inserted into the text. K9 tries to scale the image to the available screen width so that it is displayed completely. As a result, the font size is reduced relative to it.
the email contains a (relatively long) link. K9 apparently cannot create a line break in a link, but displays it in its full length on a single line. As a result, the font size is also reduced relative to it.
The app “Bluemail” at least has a button that can be used to switch the display and make it much more readable. I am not aware of such a button in K9. However, I would like to see an option that automatically optimizes the displayed font size.
Thanks and greetings