I've been using another email app for a long time now, but would like to use Thunderbird, however there are a few little things that are annoying about the current version compared to my existing app.
I would like the message header information to take up less space. Attached is a screenshot of Thunderbird vs my current app. As you can see, there is a vast amount of IMO wasted space showing header information. The current app can toggle between compact and expanded by tapping on the header.