Hello
is there a way to make kmail show the value from between the < > of the "to" header field?
At the moment the following email would be shown as "name" but I'd like to read "name@email.com" or "name <name@email.com>"
To: name <name@email.com>

If you mean in the message list, I think it's dependent on the theme. IIRC the question was already mentioned but I'm not sure this exact functionality is available.

So how could I create an own theme? The drag & drop editor is clearly not sufficient for that purpose. Is there maybe a config file or something?

The templates use the Django template format. I'm not sure you can create one from scratch: I'll ask around.