It would be nice to have a feature in #Thunderbird, that allowed me to enter default account settings so I wouldn't have to manually adjust them with every single new account that I add to thunderbird (which are quite a few).
Also a synchronization functionality, like in Firefox, is long overdue. I have (at least) three PCs, that I regularly use, most of them with several OS to switch, so I have to maintain at least 5 or 6 installations of thunderbird.