Exchange service for Extranet users

Hi,

We are now in the process of planning and designing Microsoft Exchange. We have 2000 internal users
and about 4000 external users which are our independent stores and should have Exchange mailbox.

We have security and access challenges for our 4000 extranet users. We want to give them mailbox, OWA and POP3 access but at the same don't want to give them access on our active directory environment.

Which strategy you guys recommend for our environment?

Regards,

NetRock