The Simple Mail Transfer Protocol (SMTP) service processes incoming traffic from SMTP clients such as Microsoft Outlook Express and other SMTP hosts. It sends outbound SMTP traffic using configured SMTP Connectors and Routing Group Connectors.
The SMTP service is a key component in Exchange 2000 because it is the primary protocol for communicating with other computers running Exchange 2000, replacing the remote procedure call (RPC). It is also a key protocol for transferring e-mail over the Internet and providing interoperability with other e-mail systems.

Note In previous versions of Exchange, the Internet Mail Service provided the SMTP engine features. The Windows 2000 SMTP service, which is a component of IIS, now provides these functions.

When you use the SMTP service with Exchange, the following changes to the SMTP service will occur:

• Messages destined for a local domain are now transferred by default to Web Storage System instead of a drop folder.
• Exchange System Manager configures the SMTP service. Exchange System Attendant applies this configuration, which is stored in Active Directory, to IIS.
• Exchange System Manager uses an SMTP service application programming interface (API) to display the status of mail messages queued for delivery.

• The SMTP Process
• SMTP Directories
• SMTP Transport Architecture
• Managing Messaging Delivery for SMTP
• SMTP Extensions
• Managing SMTP Virtual Servers