Small companies usually need an Internet connection to send their electronic messages, but their email volume might not justify the expense of a dedicated line. When you don't need 24-hour email connectivity, ETRN support in Exchange Server's Internet Mail Service (IMS) offers a fast, easy solution for Internet connectivity. This SMTP command lets you use your Exchange server to periodically connect to an ISP to send and retrieve your SMTP mail.
To take advantage of ETRN's functionality, you need to understand how ETRN works and how to configure it. In this discussion, I assume that you're using Exchange Server, except where I state otherwise.
ETRN Concepts
Exchange Server 5.0 Service Pack 1 (SP1) added ETRN support for SMTP connectors, and Exchange Server 5.5 incorporated ETRN in the IMS. Before Microsoft enhanced ETRN, you used the TURN command (another SMTP command) to extend SMTP to quickly dial up an ISP, transfer mail, and disconnect. However, TURN initially had a security hole: It couldn't authenticate the client. The result was that a clandestine host could impersonate a valid SMTP server and download someone else's mail. Microsoft uses ETRN as an enhancement to provide authentication. . . .
Register
Anton Largiader December 15, 2003