I have been using Thunderbird for a month or so now and am finding it a great alternative to the other mail clients out there!
One thing I'd like to suggest is easier filtering of starred emails. Currently, when looking at an inbox, I have to first select 'Quick Filter', then open the Quick Filter menu, then select 'Starred' to see these. It would be great if this could be done in one step, instead of three!
Just a suggestion. Maybe I'm missing something though - if so, let me know. Keep up the great work. Thanks!