English: #b1gMailServer on a managed server without root? Yes, that is possible.
On @hostsharing there is a guide how to use b1gMailServer POP3 and IMAP. Thanks to the #Hostsharing members for their help with systemd and the @luki for providing a managed server for testing.
The guide (in German): https://wiki.hostsharing.net/index.php?title=B1gMail