sbs 2003 - are CALs needed just for exchange mailboxes?

say we have 5 people in house / using sbs 2003.  BUt there's a bunch more people outside that want to get their mail.  Currently we are using an outside email / web host.  the in house users get their mail with the pop connector.  the outside people use webmail from the outside company.  that way we only need 5 cals.

but people inhouse sending to the outsiders can't get their mail to them - there's no exchange mailboxes for those people.  is there a way to force inhouse mail to our own domain to go to the outside host for just the outsiders or even for everyone (yeah that would be goofy - send a message to next cube and it goes out to the internet to come back in, even with the exchange server).  because if we create mailboxes for all users, even the outsiders to redirect to a web mail box, would that use CALs?  They never come in the office, never log into the SBS box...  we just want email to them to go to the outside hosting company, where an account for them DOES exist.

thanks!