I have two Domains. One for email and another for user Authentication. I plan to migrate exchange to the user authentication domain. How do I retain my mailbox enabled users and still move to new Domain with a different login name. (My user authentication name is user@local) while my email enabled mailbox is user@email.com. I still want to retain user@email.comMathew Muthama MCP, MSCA

Hi, You can backup mailbox database file on Exchange 2003. Move the mailbox to exchange 2010. restore the backup on Exchange 2003, all the mailbox should be disconnected then you can reconnect the mailbox to another user.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.