Hello Jon, You need to create a recipient policy in Exchange for new domain and add the MX record for other domain in DNS. Reference: How do I configure my Exchange 2000/2003 server to accept e-mails for domains other than my own?

hi jon, i can't understand your meanning :"two domain"means two domain envor two domain name space? if it's two name space , amit tank has provided exactly reply; if it's two domain env , a single exchange server can't accomplish your goal; if it 's wrong for me to understand your meanning , please free time to let me know; thanks; -Jack