What
is qmail?
qmail is
an Internet Mail Transfer Agent (MTA) for UNIX-like operating
systems. It's a drop-in replacement for the Sendmail system
provided with UNIX operating systems. qmail uses the
Simple Mail Transfer Protocol (SMTP) to exchange messages with MTA's
on other systems.
3.
Why use qmail?
Your
operating system included an MTA, probably Postfix or Sendmail,
so if you're reading this document you're probably looking for
something different. Some of the advantages of qmail over
vendor-provided MTA's include:
3.
Security
qmail was
designed for high security. Sendmail has a long
history of serious security problems. When Sendmail was
written, the Net was a much friendlier place. Everyone knew everyone
else, and there was little need to design and code for high security.
Today's Internet is a much more hostile environment for network
servers.Sendmail's author, Eric Allman, and the current
maintainer, Claus Assman, have done a good job of tightening up the
program, but nothing short of a redesign can achieve true security.
3.2.
Performance
qmail parallelizes
mail delivery, performing up to 20 deliveries simultaneously, by
default.
3.3.
Reliability
Once qmail accepts
a message, it guarantees that it won't be lost. qmail also
supports a new mailbox format that works reliably even over
NFS without locking.
3.4.
Simplicity
qmail is
smaller than any other equivalently-featured MTA.
4.
History
The
first public release of qmail, beta version 0.70,
occurred on January, 24, 96. The first gamma release, 0.90, was on
August, 96.
Version
0, the first general release, was announced on February, 20, 97. The
current version, 03, was released on June, , 98.
5.
Features
The qmail web
page, http://cr.yp.to/qmail.html,
has a comprehensive list of qmail's
features. This section is based heavily on that list.
5.
Setup
Automatic
adaptation to your UNIX variant--no porting needed
Automatic
per-host configuration
Quick
installation--no big list of decisions to make
5.2.
Security
Clear
separation between addresses, files, and programs
Minimization
of setuid code
Minimization
of root code
Five-way
trust partitioning--security in depth
Optional
logging of one-way message hashes, entire message contents, etc.
(See What
is QUEUE_EXTRA? in Appendix E.)
5.3.
Message construction
-
Full
support for address groups
Automatic
conversion of old-style address lists to RFC 822 format
sendmail command
for compatibility with current user agents
Header line
length limited only by memory
-
-
-
5.4.
SMTP service
-
8-bit clean
RFC
93/ident/TAP callback--can help track spammers/forgers
Relay
control--stops unauthorized relaying by outsiders
No
interference between relay control and aliases
Automatic
recognition of local IP addresses
Per-buffer
timeouts
Hop
counting
-
Refusal
of connections from known abusers (via ucspi-tcp)
Relaying
and message rewriting for authorized clients
Optional
RBL/ORBS support (via rblsmtpd)
5.5.
Queue management
Instant
handling of messages added to queue
Parallelism
limits
Split queue
directory--no slowdown when queue gets big
Quadratic
retry schedule--old messages tried less often (see Appendix
E)
Independent
message retry schedules
Automatic
safe queueing--no loss of mail if system crashes
Automatic
per-recipient checkpointing
Automatic
queue cleanups
Queue
viewing (See qmail-qread)
-
5.6.
Bounces
5.7.
Routing by domain
Any
number of names for local host (See locals)
-
-
-
UUCP
hook
5.8.
SMTP delivery
5.9.
Forwarding and mailing lists
-
-
-
-
Mailing
list owners--automatically divert bounces and vacation messages
VERPs--automatic
recipient identification for mailing list bounces
Delivered-To--automatic
loop prevention, even across hosts
5..
Local delivery
User-controlled
address hierarchy--fred controls fred-anything mbox delivery
Reliable
NFS delivery (See maildir)
User-controlled
program delivery: procmail etc. (See qmail-command)
Optional
new-mail notification (See qbiff)
Optional
NRUDT return receipts (See qreceipt)
Conditional
filtering (See condredirect and bouncesaying)
5..
POP3 service
-
UIDL
support
TOP support
APOP hook
-
6.
Related packages
qmail follows
the classic UNIX philosophy that each tool should perform a single,
well-defined function, and complex functions should be built by
connecting a series of simple tools into a "pipeline". The
alternative is to build more and more complex tools that re-invent
much of the functionality of the simpler tools.
It's
not surprising, then, that qmail itself doesn't do
everything everyone might want it to do. Here, then, are some of the
most popular add-ons written for qmail. Of course, many
standard UNIX utilities can also be plugged into qmail.
dot-forward--a Sendmail .forward file
compatibility add-on
fastforward--a Sendmail alias
database compatibility add-on
-
daemontools--a
set of tools for managing daemons and their logs
-
-
mess822--tools
for parsing Internet mail messages
ezmlm--a
mailing list manager for qmail
7.
Architecture
Appendix
D covers qmail's
functional and physical structure. In a nutshell, qmail consists
of a series of programs (modules) that perform different tasks.
8.
License
As
of 2007--30, qmail 03
is in the public domain. See http://cr.yp.to/qmail/dist.html.
This means that there are no legal limits to what you can do with it:
you can copy it, give it away, sell it, modify it, rename it, or use
pieces of it in copy-protected works, without any restrictions.
9.
Comparison with other MTA's
A
book could be written about this topic, but it would be tedious
reading. Here's a quick comparison of qmail with
some of the most common UNIX MTA's.
MTA
|
Maturity
|
Security
|
Features
|
Performance
|
Sendmailish
|
Modular
|
qmail
|
medium
|
high
|
high
|
high
|
addons
|
yes
|
Sendmail
|
high
|
low
|
high
|
low
|
x
|
no
|
Postfix
|
medium
|
high
|
high
|
high
|
yes
|
yes
|
exim
|
medium
|
low
|
high
|
medium
|
yes
|
no
|
Courier
|
low
|
medium
|
high
|
medium
|
optional
|
yes
|
Sendmailish means
the MTA behaves like Sendmail in
some ways that would make a switch from Sendmail to
the alternative MTA more user-transparent, such as the use
of .forward files, /etc/aliases,
and delivery to /var/spool/mail.
.
Documentation
.
man pages
The qmail distribution
comes with a complete set of man pages.
After installation, they're in /var/qmail/man.
You'll probably need to add that directory to your MANPATHenvironment
variable.
Shell
|
Command
|
Bourne (/bin/sh)
|
MANPATH=$MANPATH:/var/qmail/man; export
MANPATH
|
bash, Korn
|
export MANPATH=$MANPATH:/var/qmail/man
|
C Shell
|
setenv MANPATH $MANPATH:/var/qmail/man
|
At
this point, commands in the format "man name-of-qmail-man-page"
should display the appropriate man page.
The man pages
are also available on-line in HTML format from:
Note: The qmail man
pages are loaded with information, but they require careful reading
because they're written in a very dense, technical style. You might
want to print off a set and read them through once to familiarize
yourself with what's there and where it is. Very little information
is repeated on multiple pages, so if you don't know where something
is covered, it can be hard to find it.
.2.
Docs
The qmail distribution
includes a series of documents that are installed
under /var/qmail/doc.
They include:
FAQ:
Frequently Asked Questions, with answers
INSTALL*:
Installation documentation
PIC.*:
Descriptions of how qmail performs
key tasks. See the Architecture appendix
for more information.
Various
other installation-related documentation
These
docs are also available on-line from:
.3.
FAQs
There
are two official FAQ (Frequently Asked Questions, with answers)
documents:
The
web FAQ is more complete.
.4.
Books
.4. The
qmail Handbook
Dave
Sill, the author of Life
with qmail,
has written a qmail book
for Apress (http://www.apress.com/).
This book, The
qmail Handbook,
covers everything in this guide, but goes into much more detail and
also covers a lot of new ground.
.4.2. Qmail
Quickstarter: Install, Set Up and Run your own Email Server
Kyle
Wheeler has written a qmail book
for Packt (http://www.packtpub.com/).
As the title suggests, this book is designed to help people new
to qmail to
set up a mail server.
.4.3. qmail
.4.4. Running
qmail
Richard
Blum has written Running qmail, which is published by
Sams. This book has received mixed reviews on the qmail mailing
list.
.4.5. qmail:
Yuksek Performansli E-Posta Sunucu
.5.
List archives
The qmail e-mail
mailing list, maintained by Dan Bernstein, is a valuable source of
information. Web archives of the lists messages are kept at:
Most
questions about qmail can be answered by searching
the list archives first.
.6.
Other Web Sites
-
http://www.qmail.org:
the unofficial qmail home
page. Contains lots of information about add-ons and patches, and
links to many good qmail web
pages on other sites.
-
.
Support
.
Mailing lists
The
following lists reside on list.cr.yp.to. In order to prevent
harvesting of e-mail addresses by spammers, I'm avoiding the use of
complete, valid addresses and "mailto" URL's.
The
lists are managed by ezmlm, which uses different
addresses to perform different functions:
listname@list.cr.yp.to:
the submission address. Messages sent here go out to all members of
the list. Do not send
subscribe/unsubscribe requests here: they won't work, and they'll
annoy the subscribers.
listname-help@list.cr.yp.to:
the "help" address. Returns a list of command addresses
and general usage information.
listname-subscribe:
send a blank message here to subscribe.
listname-unsubscribe:
send a blank message here to unsubscribe.
To
specify a subscription/unsubscription address, say joe@example.com,
send the message to:
. qmail
The
main qmail mailing
list. For discussion and questions/answers on most things related
to qmail,
except those with their own lists. Read Charles Cazabon's "
Steps to qmail List Bliss"
at http://pyropus.ca/personal/writings/-steps-to-qmail-list-bliss.html before
posting. Also read the FAQs and search the list
archives before posting a question. When you ask questions,
please try to include sufficient details to make it possible for
people to respond:
What
did you do? What's
your configuration? Include qmail-showctl output
if you're not sure what's important. What action did you take? If
this is a new installation, tell how you installed qmail.
What
did you expect to happen? What was the outcome you were
trying to achieve? Don't assume the reader can guess.
What did happen? Describe
the actual result. Include log file clippings and copies of
messages, with headers.
Note: The qmail list
uses a utility called qsecretary to
verify that messages posted to the list are not spam. Each message
posted to the list will result in an e-mail confirmation request
from qsecretary.
Read the message and follow the directions to confirm your
message--usually just replying to the qsecretary message
will do the trick. Regular list posters often automate this process
using autoresponders like Charles Cazabon's pymsgauth,
available
fromhttp://pyropus.ca/software/pymsgauth/. pymsgauth verifies
that message sent to the qmail list
really came from you, so it won't automatically confirm forged
messages sent to the list in your name.
.2. qmailannounce
The qmail announcement
mailing list. New releases are announced here. There's no submission
address: it's a read-only list.
.3. serialmail
For
discussion of the serial mail package.
.4. ezmlm
For
discussion of the ezmlm mailing list manager.
.2.
Consultants
.3.
FAQTS Knowledgebase
A
database of qmail-related
questions and answers is available at http://qmail.faqts.com/.
If you have a question that the FAQ doesn't answer, try searching
this knowledgebase. It's especially good at answering "how to"
questions
