Configuring ETRN on the Server and the Client Essay
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To set up ETRN, you need to configure the server and the client separately. The ISP usually configures the server side. The setup is simple if your ISP is using Exchange Server. Go to the Connections tab of the IMS property sheet. Under Message delivery, click E-Mail Domain. Add the customer’s domain name and select the Queue messages for ETRN check box, as you see inScreen 1. If you don’t check this box, the ISP server will immediately attempt to deliver messages even though the ETRN client is offline.
Checking this box prevents unsuccessful retries and nondelivery reports (NDRs) back to the originator. ISPs that don’t use Exchange Servers can configure the Sendmail utility for ETRN capability. The ETRN client requires more complex configuration. First, configure when the ETRN client sends mail. If you’re using RAS, be sure you’ve configured the RAS client and a phone book entry pointing to your ISP before you begin.
From Exchange Server, go to the IMS property sheet to configure your connector for ETRN dial-up.
From the Dial-up Connections tab, which Screen 2 shows, choose the appropriate remote access entry from the Available connections window. Next, decide on a schedule for calling your ISP. As Screen 2 shows, you have several options, including transferring mail at specific intervals or whenever mail is queued up. Note that you don’t explicitly define when to close the connection. The IMS terminates the connection depending on the setting in the Time-out after X min window. This parameter refers to idle time; the connection closes after the number of minutes you specify have passed. Your ISP must be able to dequeue your inbound mail within this period, or the connection will close prematurely. The connection might close if the dequeue process doesn’t proceed in a timely fashion after you’ve established the connection with the ISP.
You can accommodate a slow start of the dequeuing process by increasing the time value. You configure logon validation for the dial-up connection by clicking Logon Information on the Dial-up Connectors tab. On the screen that opens, enter your username, password, and domain (if appropriate). This information (which your ISP gives you) provides the credentials for ETRN to match against the server and provides security between the two servers. To configure ETRN to let your ISP send your mail to you, click Mail Retrieval to get to the screen that you see in Screen 3. Click Retrieve mail using ETRN. To specify the proper Internet domain, you can use the Routing property page (from the IMS property sheet) or hard-code your domain names by selecting Use these domains and entering domains in the window.
The latter option signals the ISP to dequeue messages from this domain only. If you’ve defined subdomains, precede the domain name with an at (@) character to collect mail for all domains. Subdomains let you partition companies into operating units with separate email addresses. For example, the NCR.com Internet domain has several subdomains, such as daytonoh.NCR.com and columbiasc.NCR.com. If your ISP has defined separate hosts for inbound and outbound messages, you can select Send ETRN to specified host instead of outbound mail host and define the IP address of the inbound host. If your service provider uses the TURN command instead of ETRN, you can click Issue TURN after delivering outbound mail. If you use this option, your ISP might need to authenticate your identity, if the ISP has this functionality.
You can configure these credentials (e.g., name and password) on the Security tab of the IMS property sheet. This authentication usually uses the AUTH LOGIN ESMTP extension to send the account and password on the outbound connection. If your ISP uses UNIX instead of Exchange Server, you can use the UNIX Sendmail application to dequeue messages from the ISP’s SMTP gateway for delivery to the ETRN client. To configure Sendmail, select Custom command to invoke a script that uses the Sendmail function. You enter the script in the window next to the option. For instance, the remote shell command (Rsh) causes Sendmail to run at the service provider after you’ve established a connection.
For example, the syntax Rsh I isp.com l logonalias “/user/lib/sendmail q R NCR.com” starts the remote shell, then connects to a service provider called ISP.com. The logon alias starts the shell at the ISP (this alias must match the rhosts file on the ISP). The rest of the command executes the remote shell and sends the queue to the specified domain (NCR.com). The final step in the client portion of ETRN setup is to configure your server to queue mail in the IMS for later transfer to your ISP via ETRN. On the IMS Connections tab, which Screen 4 shows, selectForward all messages to host under Message Delivery, and then enter your ISP’s IP address. Check the Dial using check box, and be sure the correct RAS phone book entry appears in the adjacent window.