Newbie question

[Allister Gearon]

Hi all,
    I am trying to configure Cyrus-IMAP (version 2.1.12), and I am a little
confused.  As I understand it one of the main advantages of the Cyrus mail
server is that the server is a sealed server.  Do I undestand correctly from
this that the users do not have to be created on the OS of the Cyrus mail
server, that the mailboxes just have to be created via the cyradm tool.  Or
is that you create the users on the OS but just don't provide them with a
shell?
Thanks in advance
Al