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<TITLE>Developer.com - Online Reference Library - 0672311739:RED HAT LINUX 2ND EDITION:SMTP and POP</TITLE>
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<!-- TITLE=RED HAT LINUX 2ND EDITION //-->
<!-- AUTHOR=DAVID PITTS ET AL //-->
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<!-- PUBLICATION DATE=1998 //-->
<!-- CHAPTER=07 //-->
<!-- PAGES=0097-0130 //-->
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<A NAME="PAGENUM-128"><P>Page 128</P></A>
<P>To see that sshah was in fact added, you type
</P>
<!-- CODE SNIP //-->
<PRE>
[root@mtx /root]# popauth -list
sshah
</PRE>
<!-- END CODE SNIP //-->
<P>If you need to remove the user sshah, use the
-delete option like this:
</P>
<!-- CODE SNIP //-->
<PRE>
[root@mtx /root]# popauth -delete sshah
</PRE>
<!-- END CODE SNIP //-->
<P>Warning: You will not be prompted for confirmation when deleting users from this database!
</P>
<H4><A NAME="ch07_ 41">
Managing Bulletins
</A></H4>
<P>Occasionally, you might need to send mail to all your users to alert them about changes to
the system. (For example, you might send this message:
The servers will be offline on Sunday for
maintenance.) If most of your users use POP to read their mail, using bulletins will
be much easier on your system.
</P>
<P>A bulletin is a message that is sent to all users as they log in to read their mail. It isn't
delivered to the users' server mail queues unless they have elected to keep their mail on the server
instead of downloading it. By using bulletins for announcements instead of sending out mail, you
can reduce the load on your mail server because it doesn't have to perform delivery to all your
user's mail queues. Even better, this approach doesn't waste space on your server because the
message is directly downloaded to the readers' machines.
</P>
<P>To create a bulletin, simply create a new file in the
/var/spool/mail/bulletins directory (or directory of your choice if you use the
-b option on in.qpopper) with the filename
beginning with a number, followed by a period, and then any arbitrary string. Consider this example:
</P>
<!-- CODE SNIP //-->
<PRE>
1.welcome_to_our_pop_server
</PRE>
<!-- END CODE SNIP //-->
<P>This bulletin could be the first one on your system. Each new bulletin must follow the
numbering pattern in sequence. So the next bulletin, for example, could be titled
</P>
<!-- CODE SNIP //-->
<PRE>
2.notice_of_downtime
</PRE>
<!-- END CODE SNIP //-->
<P>Inside each file must be the necessary e-mail header information so that the client POP
readers know how to handle the message. A minimal header consists of only a
From line; however, the users will receive mail that appears to come from no one, with no subject, and no return
address. Hence, better mail headers contain not only the
From line, but also lines for the From:, Date:,
Subject:, and Reply-To: headers.
</P>
<P>The following is a sample message:
</P>
<!-- CODE //-->
<PRE>
From sshah@domain.com Tue Sep 16 20:31:15 1997
From: sshah@domain.com (Steve Shah)
Date: Tue, 16 Sep 1997 20:31:15 -0700
Subject: New compute server
Reply-To: sysadmins@domain.com
</PRE>
<!-- END CODE //-->
<A NAME="PAGENUM-129"><P>Page 129</P></A>
<!-- CODE //-->
<PRE>
Hello Everyone,
For your information, we have finally set up the new dual processor compute server.
(The old single processor server was getting lonely. ;) If you have any questions
or problems, feel free to send me mail or call me at x9433.
-Your Systems Group
</PRE>
<!-- END CODE //-->
<P>After the file is in place, you do not need to alert the server because the server
automatically sees the file and sends it to all users as they log in to read their mail.
</P>
<H3><A NAME="ch07_ 42">
Summary
</A></H3>
<P>In this chapter, you learned how to install, set up, and configure the
sendmail and qpopper programs. The key things to remember about this process are the following:
</P>
<UL>
<LI> An MTA is a Mail Transfer Agent (what actually routes and delivers mail), and
an MUA is a Mail User Agent (what the user uses to access her mail once it has
been delivered). sendmail is an MTA only.
<LI> The Simple Mail Transfer Protocol (SMTP) is the actual protocol used to
transfer mail. sendmail is a program that uses this protocol to communicate with other
mail servers. Other mail servers don't need to run
sendmail, but they do need to communicate via SMTP.
<LI>
sendmail does NOT deliver mail once it has reached the destination system. A
special program local to the system such as
/bin/mail or /usr/bin/procmail is actually used to perform the delivery functions.
<LI> The aliases file can either remap e-mail addresses to other usernames, redirect mail
to files, or pass e-mail messages on to another program for processing.
<LI>
sendmail is a large program with a past history of security problems. Hence, be sure
to keep u with the security bulletins.
<LI> Whenever a new version of
sendmail is released, download it from
ftp.sendmail.org and install it.
<LI> The Post Office Protocol (POP) is a protocol for allowing client machines to
connect to a mail server and transfer mail. POP is not responsible for delivering mail to
other users or systems.
<LI> Although POP isn't nearly as large or complex as
sendmail, it does have the potential to contain security problems as well. Watch for security announcements and
upgrade accordingly.
<LI> Bulletins are a handy way to distribute mail to all of your POP mail users at
once without having to make copies for everyone.
<LI>
popauth is the means by which the POP protocol accepts passwords in an
encrypted format.
</UL>
<A NAME="PAGENUM-130"><P>Page 130</P></A>
<P>Telling you all you must know about SMTP and POP in a single chapter is not possible,
but as Yogi Berra (or maybe Casey Stengel) once said, "You could look it up," and you
should. However, this chapter should give you a good basis for understanding the theory behind
SMTP, V8 sendmail, and qpopper.
</P>
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