I'm using an own mail server for quite a while so I have some experience in setting up a mailserver.
For me, it's good to have a catchall for this domain so I can define the name of the mailing list, forum or any other kind before the @ sign and can identify spammers where they come from :-)

So I created a new file in /etc/postfix/ldap called
server_host = localhost
server_port = 389
version = 3
search_base = dc=domain,dc=org
scope = sub
domain = ldap:/etc/postfix/ldap/
bind_dn = uid=kolab-service,ou=Special Users,dc=domain,dc=org
bind_pw = ComeOn_I_wont_tell_you
query_filter = (&(alias=catchall@%d)(objectclass=kolabinetorgperson))
result_attribute = mail
In the kolab-webadmin page you can now add a new alias called