yeah, it is a shame apple can not get it right with their high resolution displays. So you have to use this addon. https://addons.mozilla.org/en-us/thunderbird/addon/theme-font-size-changer/

Thanks Works a treat!

I can only get the add on to change the font in the email list. but when I open an email to read it, the print is so small I can't read

Same here, I run windows and altering display settings in options, changes nothing. Even setting min font size achieves nothing at all.

Ian3145 said

Same here, I run windows and altering display settings in options, changes nothing. Even setting min font size achieves nothing at all.

right click your desktop, select screen resolution. Select make things bigger or smaller. and change the windows settings.

You might also consider contacting your correspondents and asking them to stop setting microscopic fonts in their emals

My screen resolution and text size are fine, so is the font people are using. The problem is in the Thunderbird display.

Ian3145 said

My screen resolution and text size are fine, so is the font people are using. The problem is in the Thunderbird display.

Apparently they are not. Your posting here complaining they are not fine.

They can not be much of an issue though as it has taken you weeks to re appear on someone else's issue to query the original information you were given.

On the toolbar > Options > display > Formatting > Advanced and disable allow messages to use other fonts.

Note that font sizes are in Pixels.so will be about 30% smaller than the points Microsoft used to describe sizes in Windows. They will be even smaller on Apple hardware that uses pixel doubling to make the microscopic appear normal.

If this does not satisfy you I suggest you ask your own question. I will not reply to you further here.