Various questions about SMTP and IMAP

[Mathieu Blondel]

Hi all, 

I'm running Kolab-server 1 on Mandrake 10 and I have several questions about 
SMTP, IMAP and LDAP : 

 - Is it possible to prevent a certain class of IP from sending mails through 
smtp (e.g. 192.168.0.0/16) ?
 - Were are emails stored ?
 - What is the best way to backup them ? How can I do if one day I want to 
transfer my mails to another imap system ? I guess emails are stored in a 
database so I don't know how I could do I wanted to transfer my mails to an 
imap system that uses Maildir files.
 - Currently, "Trash" and "Sent" folders are subfolders of "INBOX". Is it 
possible to put them on the same level ? 

Thank you very much for your help. 

Mathieu