When I'm using Thunderbird with a 1080p resolution, it looks so small until zoomed. Is there any way to make messages look bigger permanently? Since the last Thunderbird update text cannot be forced to have a minimum size for all the messages.
For permanent changes in Thunderbird:
In the menubar, click on Edit -> Preferences.
In the preferences window, click on "Display", and then the "Formatting" tab.
Here you can change the default font and font size for e-mail messages.
This change will be permanent for all messages (unless you change it again of course).