I pay for the Owl extension [0] which allows me to use my university's MS Exchange account with Thunderbird. I don't understand why Mozilla don't offer this themselves though, is it too complicated to put the effort in given the size of the userbase? Or is there some reason it has to be proprietary and they're against releasing proprietary software? I really appreciate Owl, but I'd much rather just pay Mozilla directly for it.
0: https://www.beonex.com/owl/