As long as they keep the current Thunderbird available, I don't think it
will matter that much if they don't develop it further. Thunderbird is very mature and the last few features they've added I've not used at all, so I won't worry about this as long as TB is still available to me to use. I like to use an email client where I get copies of my mail on my system as it's NOT always possible to get to the webmail server when I want to. I even check my Gmail accounts through TB.
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