I have Exchange 2003 Ent and Windows 2003 Ent Editions. I have an AD domain with an AD sub domain. The AD subdomain is used for another company in our building. They have their own DC. We own the other company but because of political reasons we have different IT Admins. Everything is working great. Now we want to setup Exchange Mailboxes for those users in the AD Subdomain on our exchange server? Can someone point me in the right direction? Do I need to run some of the utilities on the Exchange 2003 Setup Disk on the Sub Domains DC and add their MX record to my DNS? If not, how will they manage the Exchange Attributes for those users? I have been running Exchange for several years but never with AD Subdomains. I have searched everywhere for some pointers. I hate to buy another copy of Exchange Ent to get around this.