Hello All, I've created a new domain to take over our existing. No trust is setup between but can be if needed. In domain 1 we run Exchange 2003. In domain 2 we run Exchange 2007. I want to migrate department by department mailboxes. All external mail will come in on SMTP into Exchange 2003. So I'm looking for two things; 1. How can I configure Exchange 2003 to understand if the user/email doesn't exist in Domain 1 to forward mail to Exchange 2007 in Domain 2? Applicable to both internal and external mail. 2. With SMTP contacts within the organisation, I'd like to retain the ID's so when users reply to emails with those contacts they don't get a 'can't find' contact message returned. Thanks in advance,

Hello, Configure Cross-Forest Connectors http://technet.microsoft.com/en-us/library/bb123546(v=exchg.141).aspx Thanks,Simon Wu TechNet Community Support

Hello, Configure Cross-Forest Connectors http://technet.microsoft.com/en-us/library/bb123546(v=exchg.141).aspx Thanks,Simon Wu TechNet Community Support

Hello Simon, Thanks for the reply. I'd like to clarify both Domain 1 and Domain 2 Exchange Servers will need to maintain the same address space i.e. contoso.com . Domain 1 Exchange Server 2003 hosts the live mailboxes, reception and distribution of address space contoso.com emails. I want to migrate contoso.com to Domain 2 Exchange 2007 by department, not all departments at once. When emails are received by Exchange Server 2003 and no recipient are matched, I'd want it forwarded to Exchange 2007, where it would be matched or delivered to an 'Undeliverable' mailbox. As users are migrated to Exchange 2007 their emails addressed to recipients existing on the Exchange 2003 server need to be forwarded there. The TechNet article suggests forwarding all mail for the address space contoso.com instead of checking if forwarding is necessary. Please can you clarify the article configuration will address my requirement described above or confirm a better method of migration? Thanks and Regards, Trevor