We recently created a new site within a forest for a new office. The forest is comprised of multiple trees each of which is a single domain. The users for our new site (A) will be receiving their email from an Exchange server in another site (B). The users were created earlier in site B so that their mailboxes could be set up. However we now find ourselves in a situation where we've got a site configured, site A, but the users for that site all reside on the AD server in site B.
Is there any way to copy/move our site A users to site A from B, without affecting their mailboxes in site B? We would like the users to have a local office login and not experience the lag of logging in to site B from their desktops. I should add that site A is using Windows 2008 R2 while site B is using Windows 2003 and Exchange 2007.