I usually use "Smaller" for Text display size because folder pane and email list pane font gets smaller and look out more folders and emails at a glance. But in that case, font in preview gets smaller also and sometimes it's difficult to read. So could you make the feature to set smallest font size in preview pane? Actually most of case, we spend much of time reading email and small font gets tougher when you get older (40+). I can increase the text size by Cmd+'+' but in that case all the email's font gets bigger. Some html email is large enough to read. So rather just want to set minimum font size. I think I saw similar feature in other email client. Maybe setting minimum font size can be OK with text email if it's not easy for html email. And html email font size should be set to appropriate text size.