For the self-hosted folks there are: https://mailcow.email/ - dockerized, works with multiple domains, sogo for groupware. Compared to mailinabox's single disk, it has 6 docker volumes to keep track of. https://mailu.io/ - dockerized, it has a section on kubernetes deployments, which i find weird, but I guess could make sense for companies https://mailinabox.email/ - no docker, no multiple domains, roundcube, nextclo…
Are you sure? I am running mailinabox and have multiple domains and accounts with no issue.