I think you want to utilize an Exchange Resource domain to host email:
http://www.msexchange.org/articles_tutorials/exchange-server-2007/planni ng-architecture/deploying-exchange-resource-forest-part1.html This might not be the right Exchange version for you but it should point you in the right direction. mb From: Lynden A. Philadelphia [mailto:[EMAIL PROTECTED] Sent: Thursday, October 30, 2008 8:03 PM To: MS-Exchange Admin Issues Subject: Two Domains One Exchange Server Does anyone have any documentation on how to setup Two Domains with one Exchange Server. Company A and Company B Merged. Both are Windows 2003 A/D. There is an External Trust relationship between the two Domains. Now Company A is installing an Exchange Server and Company B doesn't want to buy there own. How do we give access to Company B users? Thanks in advance. L This message is intended for the use of the individual or entity to which it is addressed and may contain information that is privileged, confidential and exempt from disclosure under applicable law. If the reader of this message in not the intended recipient or the employer or agent responsible for delivering the message to the recipient, you are hereby notified that dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please notify me immediately by email or telephone, and delete this message and all of its attachments. Thank You. ~ Ninja Email Security with Cloudmark Spam Engine Gets Image Spam ~ ~ http://www.sunbeltsoftware.com/Ninja ~