Try View>font size

Thanks, still looks quite different but at least it's easier to read.

Same thing here since the update. making the font bigger makes all the fonts on the page bigger. It's really only the font in the inbox window that got proportionally smaller. Can we just make the text in the inbox window bigger.

These steps may address your concern if it's the email message font that you want to change:

- in Tools>settings>general, set your default font. 
- then click the advanced button. Notice the drop-down menu at top. It probably says 'latin' or 'other writing systems' - this is IMPORTANT: 
- select 'latin from that menu, set your desired font and font size settings, click OK, 
- select 'otherwritingsystems' from the drop-down menu and set the IDENTICAL settings to what you did for Latin, and then click OK. 
- and, if you have account set to compose HTML, then set that in tools>settings>composition to variable-width and medium font. (You would only change the HTML font setting if your intent is for recipient to receive your preferred font - not my personal recommendation.)
- Set Sending Format to 'automatic' 

The settings are in pixels, not points, so you may need to use higher numbers. And remember to set the minimum font size as well.

I have been playing around with this for ages, and the answer is actually very easy. Go to View, then Font Size - you can increase the size of your inbox messages. HOWEVER, still in View, you can go to Density -> Relaxed, which opens up the spaces beautifully. Then you can readjust font size.

I hope they don't make these kind of changes again...

That feature increases all the font sizes in all panes. The request was only for messages. And, in the default setting, the font size of sent messages is typically smaller than the font size of messages being composed.