Hi All, We currently have Exchange 2003 and will be migrating to 2010. However, we also want to create a new AD forest with a new name space and move all mailboxes to this new domain forest. We installed exchange 2010 and we tested that it works properly on the new domain.There is Two Way Forest trust established. Now, i want to know how to allow a user on the old domain to send mail to another user on the new one? or what are the moving mailbox from exchange 2003 to exchange 2010 prerequisites? Does anyone have any experience of this? I think that i'll find someone to help me on this forum. I'm waiting for your answer. Thank you

http://www.thegenerationv.com/2010/03/cross-forest-migration-with-exchange_23.htmlAlan Wang

Hi, While migrating from the Exchange 2003 to Exchange 2010 you need to take care of certain steps like: 1) Administrative Rights 2) Active Directory Permission for the new users creation (if you are creating) 3) While you are migrating you should also need to take care of things like Special Identification of each users when you are moving from the existing Exchange to the new Exchange. You can move the mailboxes through the help of the cmdlets command. 4) Even after migration (Whether it will be using a tool or manually), you need to create every user profile manually and it will ask for the outlook version. 5)You also have to take care of the two way forest trust between the two exchange before migrating the mailboxes. For more elaborative stepwise migration go to http://blogs.technet.com/b/meamcs/archive/2011/06/10/exchange-2010-cross-forest-migration-step-by-step-guide-part-i.aspx Thanks