Microsoft Exchange Server stores recipient addresses in a directory. Rather than requiring a user to supply the recipient's address for each message, the user need only type the recipient's name, which Microsoft Exchange Server then resolves into a complete address. The user must supply addresses only for recipients who are not in the Address Book. Although users see only the names or the e-mail aliases in the Address Book, the directory is a database (and a service) that contains additional addressing information used by Microsoft Exchange Server for name resolution and routing purposes.
Addresses have two parts:
Site and recipient addresses are stored in the directory. Custom addresses also can be created for recipients on foreign mail systems. Microsoft Exchange Server creates a site address using the organization name and site name that you provided during setup. Because recipient addresses are created using site addresses, be sure that you have valid site addresses before you add mailboxes or connectors.
Microsoft Exchange Server defines several address types that can be present in the gateway routing table (GWART), which the MTA searches when it is routing a message to the appropriate connectors:
EX Denotes a distinguished name on Microsoft Exchange Server. This address type is searched only when a distinguished name for the recipient exists in the directory.
MS Denotes Microsoft Mail for PC Networks.
SMTP Denotes the standard Internet mail protocol Simple Mail Transport Protocol.
X400 Denotes the O/R address, which is used for addressing under the X.400 protocol.
The address types MS and SMTP are created automatically during setup. If you install other gateways, Microsoft Exchange Server also generates other address types.