I would like to setup Exchange 2007 to receive mail from eg. ABC.com DEF.com and GHI.com. Would also like to be able to send as each of the addresses as the source. I have a small company that is comprised as 3 different companies. Would like to use Small Business Server with 1 Active Directory Domain and 1 Exchange server. How can this be done?

Hi Ken, You need to create Accepted Domain for additional SMTP domain name and create Email address policy and then configure MX record for additional SMTP domain to point to your Hub/Edge transport server. This article will provide you instructions on how-to How to Configure Exchange 2007 to Accept E-Mail for More Than One Authoritative Domain http://technet.microsoft.com/en-us/library/aa996314(EXCHG.80).aspx

You may also want to add these new domains as additional UPN suffixes in Active Directory if you plan to leverage UPN sign-in for clients (via OWA, for example). This article explains how to configure it: http://support.microsoft.com/kb/243629