Kolab newbie, how do I add mail users to a kolab domain?

Hi,

I've just started recently to look at Kolab as a groupware suite and I 
must admit I've just hit a massive roadblock: I can apparently create 
kolab domains as "additional domain namespaces", but can't add mailboxes 
to these domains. I'm most likely missing the obvious, so my question(s) 
might look dumb :)
Following the instructions from 
https://docs.kolab.org/administrator-guide/configuring-the-kolab-server.html 
I went into the webadmin portal as Directory Manager and, using "Add 
Domain" link to the right of the Domains page, added a new domain named 
0adit1.local. Select Status=active. Then I went to the "Users" page and 
selected "Account Type"="Kolab User". Filled in the mandatory fields, 
then in the "Contact Information" I'm seeing the "Primary Email Address" 
greyed out, with a preset value and I've got 2 secondary email 
addresses, all 3 using the domain part of the FQDN. Since my FQDN is 
ktest1.kolab.local, the domain part used for the email addresses is 
@kolab.local.
Now, what type of user should I create to be able to use 0adit1.local 
for the mailboxes? Do I need to add an additional unit / group etc in 
the webadmin, then select the new unit in the "Organizational Unit" 
dropdown?
Running kolab-16.0.1-12.2.el7.kolab_16.x86_64 installed via RPM on 
CentOS 7.

Any pointers are welcome. Thanks,

-- 
Adi Pircalabu