qmail by John Levine

Reviewed by Major Keary

Qmail is a widely used mail transfer agent (MTA)
capable of handling mail with, literally, millions of users, but is
sufficiently compact for deployment on small Linux and Unix
systems.

This is about qmail, the book; it is not an endorsement
of the product over other MTAs. The author of the book,
John Levine, makes comparisons with sendmail, which are
mentioned in this review for the purpose of describing the book's
content. Qmail is protected by copyright, but is freely
available; the copyright requires that, in the absence of permission to
the contrary, any redistribution must be limited to unmodified source
code in the original .tar.gz format.

There is a qmail-based package, netqmail, that can
be found at
http://www.qmail.org/netqmail.
John Levine recommends netqmail to "people installing qmail
from scratch".

The book is in two parts. The first opens with a brief overview of
mail basics before explaining how qmail works—a topic that, of
necessity, involves comparison with other MTAs, such as
sendmail. The author says, "Most monolithic MTAs
have to run as super-user to open the 'privileged' port 25
for SMTP service and deliver mail to user mailboxes
that are not world-writable. Qmail uses the principle of least
privilege, which means it runs only the program that starts local
mail deliveries, qmail-lspawn, as root. All of the other
programs run as nonprivileged user IDs. … Qmail … [is
able] … to delegate management of a virtual domain to a Unix user in a
simple and secure way."

The rest of Part I is a detailed account of how to install and run
qmail,
including how to move from sendmail to qmail, with
illustrative code examples. The author includes practical advice and
instruction that extends beyond installation of the essentials. For
example, how to install procmail and where to find the source
code. There is also a chapter, Filtering and Rejecting Spam and
Viruses, that discusses 'white' and 'black' lists and provides
URLs
for useful resources.

Part II deals with advanced topics that build on the foundation
presented in Part I. Discussions are detailed, have good technical
depth, and include information about external programs—for example, how
to install and use ezmlm-idx—and discuss how to integrate
qmail
with POP and IMAP delivery. A final
chapter contains troubleshooting tips-and-tricks.

An essential resource for those who want to manage a Unix-based mail
system with qmail and a interesting read for anyone interested
in learning how email works. The writing is an excellent example of
technical communication.

John Levine: qmail

ISBN 1-56592-628-5

Published by O'Reilly, 234 pp., RRP $69.95