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Free ebook "Linux Sendmail Administration (Craig Hunt Linux Library)" Sample Chapter
Linux Sendmail Administration
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Free download Chapter 3: Running Sendmail Authoritative Answers to All Your Sendmail Questions--Specifically for Linux Administrators Linux Sendmail Administration is the most complete, most advanced guide to Sendmail you'll find anywhere. Written by one of today's most renowned Linux experts, this book teaches you, step-by-step, all the standard and advanced techniques you need to know to install, configure, and maintain Sendmail. Hundreds of clear, consistent examples illustrate these techniques in detail--so you stay on track and accomplish all your goals. Coverage includes: * Understanding Internet mail protocols and multimedia extensions * Understanding e-mail architecture and the role of Sendmail * Installing Sendmail source or a binary distribution on a Linux system * Building a Sendmail configuration using the m4 language * Analyzing and improving the Red Hat Sendmail configuration * Using Sendmail databases to customize your configuration * Understanding the sendmail.cf file and its commands * Understanding ruleset and using rewrite rules to modify addresses * Hiding usernames and hostnames * Testing and debugging Sendmail configurations * Controlling spam e-mail * Securing a Sendmail server * Using Sendmail cryptographic authentication techniques The Craig Hunt Linux Library The Craig Hunt Linux Library is a seven-book set that provides in-depth, advanced coverage of the key topics for Linux administrators. Topics include Samba Server Administration, System Administration, DNS Server Administration, Apache Web Server Administration, NFS and Automounter, and Linux Security. Each book in the series is either written by or meticulously reviewed by Craig Hunt to ensure the highest quality and most complete coverage for networking professionals working specifically in Linux environments. Running SendmailChapter 2, "Understanding E-Mail Architecture," illustrates the importance of Sendmail for a linux system. Sendmail implements the SMTP protocol for Linux Systems. It sends and receives SMTP mail for the system, and it acts as an interface between the user's mail program and the internet. These vital tasks make Sendmail a basic component of most Linux systems. Sendmail is such an essential part of a Linux system that it is usually installed by default and run at start up. If it is not installed on your system, you need to know how to install it. Additionally, you need to know how to compile the Sendmail program for those times when you want to install the latest source code distribution of Sendmail on an existing Linux system. This chapter covers both of those topics. It also examines how and why the Sendmail process runs at start-up, and you'll look at the tools used to control wheter or not starting the Sendmail daemon is part of the Linux boot process on your system. Running Sendmail at Start-UpSendmail runs in two distinct modes: real time mode for outbond mail delivery and daemon mode for collecting inbound mail and queue processing. When a mail user agent (MUA) has mail to send, it creates an instantiation of the Sendmail program to deliver that one piece of mail. If it cannot succesfully deliver the mail, it writes the mail to the mail queue and terminates. Most Sendmail processes have a very short life. THe Sendmail daemon, on the other hand, runs the entire time the sytem is running, condtantly listening for inbound mail and periodically processing the queue to deliver the undelivered mail. The Sendmail daemon, like most daemons, is started at boot time. The ps command reveals wheter or not Sendmail is running on your system: [root]# ps -C sendmail PID TTY TIME CMD 542 ? 00:00:36 sendmailThe low process ID (PID) shows that this process was started during the boot. Running this ps command on most Linux system will show that Sendmail is running because, generally, Sendmail becomes part of the boot process when you first install Linux. Many sytems are running the Sendmail daemon unnecessarily. It is not necessary to run Sendmail as a daemon in order to send mail. Running the sendmail command with the -bd option is required only if your system directly receives SMTP mail. A Linux mail client can collect inbound mail from the mailbox server using POP or IMAP and can relay outbound mail through the mail relay server without ruunig the Sendmail daemon | |||