You will only be able to setup the POP3 connector to deliver to users that appear in then console. After a migration you will find that to get them to appear in the cnsole you will need to apply a role to them as per:
http://blogs.technet.com/sbs/archive/2008/09/22/why-are-some-of-my-users-not-displaying-in-the-sbs-console.aspxYou can then configure the POP3 connector as per:
http://blogs.technet.com/sbs/archive/2009/07/01/sbs-2008-introducing-the-pop3-connector.aspx