Could someone clarify these 2 newbie questions on external pop3 download on Zimbra 5.0.2?

1) Is it possible for zimbra to download a external mailbox having aliases and internally distribute messages based on those aliases?

mailbox a123456@externalISP.com has aliases user1@mycompany.com and user2@mycompany.com
if the mailbox is downloaded, can zimbra distribute the messages to user1 and user?

2) is there a central admin configuration for external pop3 accounts?
I found a external pop3 account setup via individual user preferences page. if this is the only way, can this setup be locked (not to modifyable by user, only admin)?

best regards