POSIX user creation

[wkmail]

I am testing Kolab 3.1 and have a clean CentOS 6.5 install in a VM.

Once I got over a few hurdles such as having to install mod_ssl and the 
'/iRony/' config issue, my test setup sends/receives email, roundcube 
works fine and I have various test accounts syncing with IOS and Android 
(Note: DavDroid is awesome, you just point it at the iRony folder and it 
goes). I can create Kolab Users, Contacts etc. In short everything works 
great.

I do have one minor riddle.

If I use the WebAdmin to create a POSIX user, it looks like it wants to 
create that as a system user (with a /home/"user"  home directory). 
However, the added user doesn't show up in /home or /etc/passwd.  I do 
see an IMAP folder created in /var/spool/imap and I can send the 
resulting user email, login to RoundCube etc.

So what is the difference between a Kolab User and POSIX user with email?

Sincerely,

-bill