I'm using mailcow for year and a half now, moved to it from Kolab. It's really great and painless to manage it. The only thing missing for me is the LDAP auth,

I'm using mailcow for year and a half now, moved to it from Kolab. It's really great and painless to manage it. The only thing missing for me is the LDAP auth, something I got used to over the years with Kolab. The OP's solutions has built-in LDAP auth, so I'll give it a try.