Internet searches never returning a usable result but have to be submitted nonetheless:
How to make Thunderbird beautiful

Things I immediately change from a thunderbird default config:
1. Vertically split mail preview
2. Sort descending by date
3. Enable the quick filter toolbar (Did I remember correctly that it's not visible by default? Seems kinda weird)

Also the columns dont make that much sense to me. Columns with two rows would also be more efficient I think...