I recently changed to using Mozilla Thunderbird at work, instead of the very buggy Microsoft Outlook. One thing was annoying me slightly: each time you change folder the entries will be sorted by date oldest first. I prefer to have newest first.
Luckily everything is configurable!
Instructions here: Change the default sort for all Thunderbird folders, inc RSS
In summary, change the mailnews.default_sort_order value from 1 to 2, then “reindex” each if the folders.