webmin/sendmail/help/intro.html

<header>Sendmail Configuration</header>

<h3>Introduction to Sendmail</h3>
Sendmail is the standard Unix program for mail transport and delivery.
When a user on your system wants to send email to someone on another host,
sendmail is the program that does the actual process of delivering the
mail. Similarly, when someone on another system sends mail to one of your
users, sendmail will receive the email and store it in the user's mail
file. <p>

Sendmail is an MTA (mail transport agent) only, meaning that it does not
present any user interface to people wishing to send email. Programs like
Eudora, elm or /bin/mail that users actually interact with a called MUAs
(mail user agents). An MUA does not deliver email itself, instead it simply
passes the email on to sendmail to do the delivery. <p>

User MUAs can be run either directly on your system (MUAs like pine, elm
or /bin/mail), or on a separate host which may be a single-user PC (for MUAs
like Eudora, Exchange and Netscape Communicator). In the first case,
mail is sent be directly invoking sendmail and passing the message to it,
and received by reading the user's mail spool file. For MUAs run on other
hosts, mail is sent by connecting to the sendmail process on your system
using the SMTP protocol, and received by connecting to a separate POP3
server. <p>

<h3>The Sendmail Module</h3>
The main page of this module shows a table of icons, each for configuring
a different part of sendmail's functionality. However, the features behind
some icons may not be available, if they have not been setup in your
<tt>sendmail.cf</tt>. When installing sendmail, you can choose which features
are available by editing an <tt>.mc</tt>, which is converted by <tt>m4</tt>
into your <tt>sendmail.cf</tt>. Many features (such as Address Mapping,
Domain Masquerading and Spam Control) may not be available unless you have
enabled them at install time. <p>

<hr>