I am in the middle of a domain migration. I've used Quest Migration Manager for AD to migrate user accounts to my target domain. The problem is when users login to the new target domain, they get an error when attempting to send email. The NDR says "You can't send a message on behalf of this user unless you have permission to do so. Please make sure you're sending on behalf of the correct sender, or request the necessary permission. If the problem continues, please contact your helpdesk."
I've disabled SID filtering, I have a trust, and the cross forest users have rights to open their mailboxes, just not send. I'm assuming it's a Send As permision issue, but when in the ESM (or whatever it's called from 2010), It doesn't appear like I can add permissions from another domain to the mailbox.
How can I configure the newly migrated users to be able to send mail on their existing Exchange 2010 server? Any help would be greatly appreciated.