I fear I have to disagree:
I am not the only one with the firewall problem, see Kein Zugriff auf die Datenbank durch eGroupware und Wordpress - UCS - Univention Corporate Server - Univention Help
Egroupware user gets created in the postinst under LDAP /egroupeware/egroupware-[mailservername] with a random password in above mentioned file. If that password does not fulfill the password policy requirements, things get messy.
Standard folder schema for the EGroupware install is mentioned in /var/lib/univention-appcenter/apps/egroupware/compose/docker-compose.yml, so even if it comes from the mailserver, EGW uses those. And I was able to change those folders in my test installation successfully, so I am absolutely sure it could and should work. Please also have a look at Struktur der Mailbox ändern - EGroupware Mail - EGroupware Help Forum for details.