It's about being able to display multiple rows of info in each item of the emails/threads panel. Something that I found quite useful in Opera Mail, e.g.: https:

It's about being able to display multiple rows of info in each item of the emails/threads panel. Something that I found quite useful in Opera Mail, e.g.: https://d2.alternativeto.net/dist/s/60b72ca2-7a26-e011-b47f-0200d897d049_4_full.png?format=jpg&width=1600&height=1600&mode=min&upscale=false https://d2.alternativeto.net/dist/s/60b72ca2-7a26-e011-b47f-... In Thunderbird, when using a 3-vertical panel layout, the columns get squished (especially long subject lines). It's not a big thing, but I would gladly trade half the vertical space for the ability to fit a couple more fields, like tags and size.