TIA for any help you can provide with this situation... I have found several articles that look similar to this issue but nothing that seems to fit perfectly: I have a client who has an existing Exchange 2003 server in an "external" domain/forest. We have installed Exchange 2010 on their internal domain/forest and are ready to migrate mailboxes but I cannot find the right steps or tools. There is no existing trust relationship between the 2 forests; they are on 2 separate subnets separated by a firewall. Each user has a separate user account on each domain. The exchange 2003 server and its associated forest/domain will go away after the conversion.

as you are saying there is no trust. only option left is exmerge. you can install SP2 on ex2003 and exmerge all the mailboxes and import them in ex2010. note there is no exmerge in ex2010. you have to use import mailbox command http://www.msexchange.org/articles_tutorials/exchange-server-2010/management-administration/import-export-mailboxes.htmlThanks Uday Kiran, Senior Consultant Cyquent Technology Consultants, Dubai Please Mark as answer if it helps you

Hi jshmeister, Yes, you can use Exmerge to export mailboxes from Exchange 2003, then import to the Exchange 2010. Download Exmerge: Microsoft Exchange Server Mailbox Merge Wizard (ExMerge) http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=2743 Note: when you use Exmerge, it cannot export over than 2GB mail (You can know more information from this thread: http://social.technet.microsoft.com/Forums/en/exchangesvradmin/thread/ef380f86-87cd-4baa-96ce-544b8d8bd207 ) If you are moving to Exchange 2010 SP1, maybe you need follow this document to import: New-MailboxImportRequest http://technet.microsoft.com/en-us/library/ff607310.aspx If you want cross forests move mailboxes, you can have a read for these documents: Exchange 2010 Cross-Forest Mailbox Moves http://blogs.technet.com/b/exchange/archive/2010/08/10/3410619.aspx Prepare Mailboxes for Cross-Forest Move Requests http://technet.microsoft.com/en-us/library/ee633491.aspx Thanks, Evan Liu TechNet Subscriber Support in forum If you have any feedback on our support, please contact tngfb@microsoft.com Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.

Hi jshmelster, Any updates on this issue? Thanks, Evan Liu TechNet Subscriber Support in forum If you have any feedback on our support, please contact tngfb@microsoft.com

i would go by creating a forest root trust and do cross forest move. here are good blogs http://blogs.technet.com/b/meamcs/archive/2011/06/10/exchange-2010-cross-forest-migration-step-by-step-guide-part-i.aspx http://technet.microsoft.com/en-us/library/aa998597.aspx if you want to Global address book sync during migration you would need to use ILM you can also use third party application like Quest software. wihich will add to your cost. Dhruv