To see that sshah was in fact added, you type

[root@mtx /root]# popauth -list

sshah

If you need to remove the user sshah, use the -delete option like this:

[root@mtx /root]# popauth -delete sshah

Warning: You will not be prompted for confirmation when deleting users from this database!

Managing Bulletins

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.

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.

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:

1.welcome_to_our_pop_server

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

2.notice_of_downtime

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.

The following is a sample message:

From [email protected] Tue Sep 16 20:31:15 1997

From:    [email protected] (Steve Shah)

Date:    Tue, 16 Sep 1997 20:31:15 -0700

Subject:    New compute server

    Reply-To: [email protected]

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

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.

Summary

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:

• 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.
• 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.
• 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.
• 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.
• sendmail is a large program with a past history of security problems. Hence, be sure to keep u with the security bulletins.
• Whenever a new version of sendmail is released, download it from ftp.sendmail.org and install it.
• 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.
• 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.
• Bulletins are a handy way to distribute mail to all of your POP mail users at once without having to make copies for everyone.
• popauth is the means by which the POP protocol accepts passwords in an encrypted format.

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.