Frankly, I think it would be easier to write a GUI over mutt than to rewrite Thunderbird.
I was a heavy user of Thunderbird, but after migrating to mutt, it's basically obsolete. The only pain point is really HTML, but converting it to text is Good Enough most of the time. Outlook-produced emails still look like crap, but I can click a button and open it on Firefox.
Mutt is not only alive and kicking, there's the new NeoMutt project that is the NeoVim for Mutt. We have initial Lua scripting capabilities now.
I was a heavy user of Thunderbird, but after migrating to mutt, it's basically obsolete. The only pain point is really HTML, but converting it to text is Good Enough most of the time. Outlook-produced emails still look like crap, but I can click a button and open it on Firefox.
Mutt is not only alive and kicking, there's the new NeoMutt project that is the NeoVim for Mutt. We have initial Lua scripting capabilities now.
http://neomutt.org/