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Thunderbird is hiring for several engineering positions, all remote and full-time: https://www.thunderbird.net/en-US/careers/
I use Thunderbird for my email every day. Looking forward to what the new folks help produce!
Server run by the main developers of the project 
It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!
@brainwane I hope these new folks "fix" the MailExtensions API.
See: https://trac.torproject.org/projects/tor/ticket/31341