Qmail is one of the most popular email servers. The current release was published in 1998, and has stood unchanged ever since. It has withstood the test of time surprisingly well, and a devoted community has grown around it to contribute experience, ideas, and patches to provide new features. While there is some dispute over the claim that qmail has no security flaws yet discovered, it cannot be denied that its security track record over the last ten years is unparalleled. Qmail includes several applications, including an SMTP server, a POP3 server, a QMTP server, and several related utilities for manipulating email and email storage. Qmail has been used by or is currently used by Hotmail, Yahoo!, NetZero, Speakeasy, Qwest, PayPal, Aruba.it, and others. You can learn more about qmail at http://cr.yp.to/qmail.html and http://www.qmail.org/.
This book treats qmail more as an architecture than a mail server, and from that perspective guides the reader through the installation, administration, customization, and deployment of a qmail-based server. The book begins with a quick, minimal, step-by-step walkthrough of a bare-bones qmail server, and then introduces and explains the basic design of the qmail architecture in easily understood terms.
The later chapters of the book are devoted to using qmail to provide specific features through customization and optimization. Alternative methods of providing each feature are compared, and a plethora of example scripts are provided to demonstrate the concepts and techniques.
Chapter 1 provides a quick step-by-step guide to installing a basic qmail server on a computer without an existing mail server, using ucspi-tcp and tcpserver to provide some of the basic services that a qmail SMTP server relies upon. At the end of the chapter is an overview of the qmail architecture that is explained in the following chapters to understand how qmail works and how the structure lends itself to customization.
Chapter 2 and Chapter 3 mirror each other: the former details how email enters the qmail queue, and the latter details how email leaves the qmail queue. The discussion of inbound mail includes the basic architectural details as well as discussion of authentication and the two protocols that qmail supports: SMTP and QMTP. The discussion of outbound mail also includes the basic architectural details and expands into basic filtering, the definition of users and mailboxes, and remote delivery.
Chapter 4 examines in detail the storage formats that qmail supports. Specifically, it covers the factors that influence the choice of the format to be used for a given situation, using mbox, Maildir, and MH as examples. One of the most common things to do with email is to retrieve it from a central server either via the POP3 or IMAP protocols, or via a webmail interface. The latter half of this chapter covers all three, and discusses the reasons for choosing one protocol over the other, how to choose an IMAP server package, and how to set up qmail's own POP3 server.
Chapter 5 begins the more advanced section of the book with a discussion of server virtualization. Multiple kinds of virtualization are discussed, including qmail's built-in virtual domain and virtual user framework, virtual domain management software, and the possibilities provided by having multiple qmail installations.
Chapter 6 unleashes the full power of the qmail architecture's design. By altering the flow of mail through the architecture—or changing the architecture itself—qmail can be made to perform virtually any task. Sending mail without a queue, blocking viruses, detecting spam, validating recipients, and using SPF and/or DomainKeys are all used as examples in this chapter. Both lightweight and heavyweight methods of spam and virus prevention are also discussed in detail.
Chapter 7 looks at some advanced features that don't quite fit into other, larger categories, such as SSL support and optimization for mailing-list delivery.
Chapter 8 covers ongoing maintenance, monitoring, and good administrative behavior. It provides a detailed description of the log files and how to interpret them and use the qmailanalog package to get statistical analysis of qmail's behavior. Expanding the log files to contain more information, identifying and recognizing problems (including "silly-qmail" syndrome), and using information in the logs to improve qmail's performance are all explored in this chapter.
Qmail works on practically all UNIX systems: AIX, BSD/OS, FreeBSD, HP/UX, Irix, Linux, NetBSD, OpenBSD, OSF/1, SunOS, Solaris, etc. It automatically adapts itself to new UNIX variants.
Qmail does not support Windows.
This book is targeted at System Administrators familiar with Linux/UNIX and DNS servers who need to set up qmail.
In this book, you will find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.
There are four styles for code. Code words and files in text that are not editable are shown as follows: "Qmail's SMTP server, for example, cannot talk to the network by itself; this ability is provided by software like inetd or tcpserver or similar." Code words and files in text that are editable are shown as follows: "Qmail comes with a set of minimal install instructions, in a file named INSTALL."
A block of code will be set as follows:
#!/bin/sh # Using splogger to send the log through syslog. # Using qmail-local to deliver messages to ~/Mailbox by default. exec env - PATH="/var/qmail/bin:$PATH" \ qmail-start ./Mailbox splogger qmail
Any command-line input and output is written as follows:
chown root ~alias/.qmail-root
chmod 644 ~alias/.qmail-root
New terms and important words are introduced in a bold-type font. Usernames have been introduced in an italicized format as follows: "However, qmail does not deliver mail to the real root user."
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