[CentOS] mail server: sendmail with integrated AD

I'm preparing my new Sendmail mail server with pop3s + smtps where user 
authentication occurs through Microsoft Active Directory by Winbind daemon.
OS is Centos 6.4 and Sendmail is 8.14
Mailboxes will be in this server but how to create them !??!
It's necessary to add user by 'useradd' command into /etc/passwd or It's 
only necessary add new entry in '/etc/aliases' file for every AD user like 
in following example ?!

mark.landers:        marklanders

- 'marklander' is the user account in Microsoft AD
- user mail is 'mark.landers at example.com'


POP3s
the account name (AD user), which I'll use to access my mailbox by pop3s, 
must have the same name of mailbox file ?
According to previous example:

if I wanted to download email of 'mark.landers at example.com', in my client I 
shall have to type 'marklanders' with its password, so my requirement is to 
have this mailbox file into my mail server:
<mail path>/<user> for example: /var/spool/mail/marklanders
I think pop3S WILL SEARCH mailbox with the same name of account name ! What 
do you think ?