Kolab / Roundcube has an interesting "Archive" button to remove the current message from the inbox. But you can still find it if needed. Cool.
However, often when I answer someone, it's clear to me that my answer is the end of the thread unless the other person replies. But sometimes, I want to keep the message in my inbox and thus keep the current behavior. Thus, I would like a "send and archive" or "reply and archive" button.