I don't know if I'm misunderstanding how it works, but in "Manage local subscriptions" I unchecked several folders because I don't even want KMail to synchronise them, when I do it they disappear, but when I restart KMail they appear again, their icon being gray:



How do I make these folders disappear?

In the case of the two [GMail] folders, that is because they don't really exist. The only reason they are shown is because folders beneath them in the folder hierarchy exist. As such they are "virtual" folders that the server doesn't know about - and which is probably causing this bug.

Oh, it works when you untick all the child folders (for instance, kde and [Gmail] in my screenshot) before unticking the parent folder. Maybe that should be done by KMail automatically?

Thank you very much!

It probably should be yes. I would recommend filing a bug report at bugs.kde.org regarding that.