We use Exchange 2000 Server, and our company just purchased another company that also uses Exchange 2000. How can we maintain separate Exchange forests but maximize interoperability between the two forests?

Maintaining separate forests while maximizing interoperability is possible but requires some work. The most common requests between separate Exchange organizations are connections for free/busy information and Global Address List (GAL) lookups. Because Exchange stores free/busy information in a public folder, you'll want to use the InterOrg Synchronization Tool, which is available as part of the Microsoft Exchange 2000 Server Resource Kit, to synchronize this special folder. GAL synchronization is a harder nut to crack. In Exchange Server 5.5, you could use scheduled directory exports and imports to easily synchronize GALs. Although you can take similar steps in Exchange 2000 and later, an easier approach is to use the GAL synchronization tools that come with Microsoft Metadirectory Services (MMS). If you don't want to use MMS, you can cheat a bit and set up an interorganization connection agreement with the Active Directory Connector (ADC); however, be aware that Microsoft doesn't fully support this method. You might also want to check out HP's LDAP Directory Synchronization Utility (LDSU). This robust utility is in widespread use (HP/Compaq uses the tool to synchronize its GALs) and is easy to administer but is expensive.