You can do that this in Hyperkitty. Setting
FILTER_VHOSTS = True
in Django's settings.py (or settings_local.py, if you are using container images) will filter the lists for the current "Host:" header in the request.
Postorius doesn't have this ability yet, but wouldn't be too much work to add that. Pull requests are welcome :)
Thanks Maxking but that did not work. I added it to the settings_local.py file, restarted the container and the same behavior prevails.