SMTP makes a connection and sends e-mail across that connection. ESMTP extends the functionality of SMTP to enable authentication, encryption, and message delivery information.
DNS supports Exchange Server 2003 by using MX records to identify e-mail servers and resolve their IP addresses.
You can create and configure additional SMTP virtual servers and SMTP connectors to control Internet access, prevent relaying, use smart hosts, and act as smart hosts.
E-mail can be held in an ISP's server and pulled to an Exchange server on demand or at scheduled intervals.
Exchange interfaces with other SMTP systems, supports IMAP4 and POP3 clients, and uses HTTP virtual servers to support WebDAV collaboration and OWA.