This is getting me anxious. See also third-party reports and comments here or there. One of the commenters mentioned Joel Spolsky, who has seen it all before as well…
Please, guys, just leave it alone. Software doesn’t rust, and you won’t do any better. Or prove me wrong with a Thunderbird2, but *without* killing the old one please. Seems we’ll have to check out Claws, even if that one doesn’t work in dark mode, at least their web site does not…