Chapter NINETEEN. An Introduction to sendmail

     

Chapter NINETEEN. An Introduction to sendmail

Chapter Syllabus

19.1 Basic Checks to Ensure That sendmail Is Installed and Working

19.2 Using sendmail without Using DNS

19.3 Mail Aliases

19.4 Masquerading or Site Hiding and Possible DNS Implications

19.5 A Simple Mail Cluster Configuration

19.6 Building Your Own sendmail.cf File

19.7 Monitoring Mail Queue

In this chapter, we introduce sendmail . The world of sendmail is vast, due primarily to the configurability of sendmail . The extent of its configurability can be demonstrated by the expanse of the documentation available for sendmail . The bible for sendmail is undoubtedly the O'Reilly and Associates book (called sendmail , funnily enough) that currently (in its 3rd edition) runs to a weighty 1,232 pages. Thankfully, the sendmail configuration file ( /etc/mail/sendmail.cf ) works well out of the box on HP-UX. We don't need to do much to get sendmail off the ground. We don't get into the format and rewriting of rulesets here; that's more the job of a specialized mail-administrator. We are going to look at some interesting features of sendmail , including looking at building our own sendmail.cf file, which includes additional features that allow us to protect our email systems against things like spamming .

sendmail starts automatically on HP-UX and acts as an MTA (Mail Transport Agent) as well as an MDA (Mail Delivery Agent). This is the job most people associate sendmail with: routing and delivering email. sendmail can be ran as an MUA (Mail User Agent), which simply means that it reads and writes your individual email messages. Most people will not use sendmail as an MUA because it is cumbersome and not user friendly. Programs such as mailx and elm are far easier to navigate. The only people I know who use sendmail as an MUA are sad, lonely individuals who don't get out much.

 root@hpeos003[]  sendmail -v root  WARNING: local host name (hpeos003) is not qualified; fix $j in config file  hello from me   .  root... Connecting to local... root... Sent root@hpeos003[] root@hpeos003[]  mail  From root@hpeos003 Thu Oct 23 13:41:54 BST 2003 Received: (from root@localhost)         by hpeos003 (8.11.1 (Revision 1.5) /8.9.3) id h9JCfm803218         for root; Thu, 23 Oct 2003 13:41:48 +0100 (BST) Date: Thu, 23 Oct 2003 13:41:48 +0100 (BST) From: root@hpeos003 Message-Id: <200310231241.h9JCfm803218@hpeos003> hello from me ?  q  root@hpeos003[] 

The warning message you saw above is one of the things we want to sort out. We are looking at the following tasks :

1. Basic checks to ensure that sendmail is installed and working.

2. Using sendmail without using DNS.

3. Mail aliases.

4. Masquerading or site hiding.

5. A simple mail cluster configuration.

6. Other diagnostic tools.

Let's get started.