I usually have this feature with the 'mailmindr' extension. It worked well, but now it's not compatible with the latest Thunderbird versions. It'd be nice to have it integrated.
Finally! Thx! I like the first approach and the feeling, and I hope you will be implementing one of the big avantages to use vertical tabs: tab grouping / tree style tabs.
I'd be very nice to have it! In our company we can't use Office365 mail with POP or IMAP, they force us to use Exchange, and people don't want to pay for an extension.
