I still use Claws Mail because I have never been able to figure out how to set Thunderbird to display emails with a consistent font size.

I've changed the advanced settings and set a minimum font size, and it has no effect. You can zoom in when you're looking at an email, but the results are inconsistent from email to email.

With Claws Mail I get the same font size every time.

If anyone knows how to set this up properly, I'd give Thunderbird a try again.