What is a SMTP?  

Simple Mail Transfer Protocol (SMTP) is the Internet standard for transporting and delivering electronic messages. Based on specifications in RFC 821 and RFC 822, Microsoft SMTP Service is included in Microsoft Windows 2000 and Exchange 2000, and uses the primary SMTP address in the default recipient policy as your organization's default domain.

Exchange 2000 Server expands the SMTP Service, enhancing the basic delivery functions of the protocol without affecting its compatibility with other messaging systems. Exchange gives you greater control over message routing and delivery, and provides secure access and channels for managing the service. Although you can make some configurations for sending e-mail to remote domains on the virtual server, you should do most of the administrative work at the SMTP connector.

If you use the SMTP Service on a computer before installing Exchange 2000, any configurations you make to the operating system for SMTP are lost. Also, messages in the Pickup or Queue directories are not delivered. In Windows 2000, SMTP uses the subdirectories in the <root>\Inetpub\mailroot directory. Although these folders aren't deleted, SMTP uses the <root>\Exchsrvr\mailroot directory.

Multiple virtual servers can be helpful in certain situations. If you have different groups of users with varying security requirements or message-size needs, you might want to create additional virtual servers. Additional virtual servers are also helpful for managing different types of e-mail. For example, in a mail gateway, one dedicated virtual server can handle Internet e-mail, while another handles internal e-mail.