Hi,
What's the correct way to make eGroupware only accessible via https?
There are two apaches running on an eBox machine. eBox's apache that runs as ebox user and is only used to server the eBox UI. By default it listens on 443. And the normal apache that is used to serve, for example, egroupware.
If you want to enable https on the normal apache, you must change first the listening port on eBox [System->General]. Now you can enable https on your normal server.