sending email

Hi I'm building a email server with suse 10.2 with postfix and courier. I
have it working .
I want give quotas to the users depending what group they belong,
Administratores, chief, users, etc.

Depending in what group they belong the size of the mailbox is diferente.

What about the size of the mails that each group can send can I especify
that users can send only 2M, chiefs can send 5M and administratores can send
10M??

Thanks
any ideia is apreciated