What is Red Hat Linux SMTP and sendmail

Even with multimedia attachments and HTML encoding prevalent in e-mail messages today, the technology behind message transfer hasn't changed significantly since the early 1980s. The framework for the Simple Mail Transfer Protocol (SMTP) was initially described in RFC 821 in 1982. The protocol itself was extended in 1993 (RFC 1425), yielding the Extended Simple Mail Transfer Protocol (ESMTP), which provides more commands and new delivery modes.

The three parts to message transfer are the Mail Transfer Agent (MTA), the Mail Delivery Agent (MDA), and the Mail User Agent (MUA). The MTA, commonly referred to as the mail server (of which sendmail and postfix are examples), actually handles distributing outgoing mail and listening for incoming mail from the Internet. The MDA accepts messages from the MTA and copies the message into a user's mailbox. Red Hat Linux uses /usr/bin/procmail as the default MDA, as specified in sendmail's configuration file. For sites that have a centralized mail server, Post Office Protocol (POP) clients are also considered MDAs. An MUA is the program run by a user to read incoming mail or to send messages to others.

sendmail MTA, the most common mail server on the Internet. Nearly 70 percent of all e-mail messages on the Internet are delivered by sendmail. With the growing Internet population, billions of e-mail messages are sent and received each day. postfix are an alternative to sendmail also.

There have been three major releases of sendmail. The original sendmail (sendmail version 5) was written in 1983 by Eric Allman, a student at the University of California at Berkeley. He maintained the code until 1987, when Lennart Lövstrand enhanced the program, simplified the configuration, and developed IDA sendmail. Eric Allman returned to Berkeley in 1991 and embarked on a major code revision, releasing sendmail V8 in 1993, which incorporated the extensions from IDA sendmail. The current version (8.12.9) is based on this "version 8" code.

Installing a mail server in Red Hat Linux is the easy part; it's the configuration that takes patience, resolve, and some experimentation. Once your mail server is running, it is easy to set up a Post Office Protocol service to allow users to download e-mail to their own workstations.

You can replace Sendmail with Postfix as your mail-transfer agent in Red Hat Linux. To make the transition a bit easier, Red Hat provides the alternatives feature. Alternatives let you to switch one MTA for another by linking essential files to the package you choose.

Sooner or later, an alias definition in /etc/aliases will become unmanageable. At this point, mailing list software, such as majordomo, can provide the flexibility necessary to manage a large distribution list, with the added benefits of archiving, moderation, digesting, and automated administration.

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Source of Information : Red Hat Linux Bible - Fedora And Enterprise Edition