I love the fact that right there on KDE.org there's a screenshot of Kontact with that big obnoxious vertical "HTML Message" black bar in the middle of the screen. I remember reading a bug report some 10 or 15 years ago to allow it to be hide-able somehow at least with the author just flat-out refusing to do it or allow patches for it.

I'll never use Kontact for this reason but I do like most of the rest of KDE.