how to handle non-win2k domain mail?

[Guest_imported]

we currently have our mail services on a Quickmail server (let's call it quickmail.org). we are getting ready to move to exchange (let's say exchange.org). exchange.org is our internal win2k active directory domain. quickmail.org is our website domain, externally controlled.

we want to move a few quickmail users over to exchange but have them still use their quickmail.org addresses... how can I set this up?

thanks,
Wes