Given that we are a communication and collaboration solution, we need to find the concepts how we want to structure communication in general, so we can apply those concepts to the various mediums (email, instant messaging, voice, video, ...), and types of communication (discussion, review, meeting, ...).

The aim of that is to get a coherent user experience no matter whether the user is using email, or instant messaging or calendar invitations etc.

A draft of such a concept can be found at https://git.kolab.org/w/ux/communication/

https://git.kolab.org/w/ux/human-communication-patterns/ backs that with a variety of known existing communication patterns.