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.
Note: The
official qmail web
page, http://cr.yp.to/qmail.html covers
the advantages of qmail more
extensively.
4. History
qmail was
written by Dan Bernstein
(DJB), http://en.wikipedia.org/wiki/Daniel_J._Bernstein,
a math professor now at the University of Illinois in Chicago. Dr.
Bernstein is also well known for his work in the field of
cryptography and for his lawsuit against the U.S. government
regarding the publishing of encryption source code.
Seehttp://en.wikipedia.org/wiki/Bernstein_v._United_States or http://cr.yp.to/export.html for
information regarding the lawsuit.
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.
The
next release is expected to be an evaluation version of 2.0. Some of
things that might appear in version 2 are covered
at http://cr.yp.to/qmail/future.html.
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
- Host masquerading (See defaulthost)
- Automatic Mail-Followup-To creation (See QMAILMFTFILE)
5.4. SMTP service
- RFC 82 RFC 23, RFC 5 RFC 52, and RFC 54 compliant
- 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
- Parallelism limit (via ucspi-tcp)
- 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)
- Detailed delivery statistics (via qmailanalog)
5.6. Bounces
- QSBMF bounce messages--both machine-readable and human-readable
- HCMSSC support--language-independent RFC 93 error codes
- Double bounces sent to postmaster
5.7. Routing by domain
- Any number of names for local host (See locals)
- Any number of virtual domains (See virtualdomains)
- Domain wildcards (See virtualdomains)
- Configurable "percent hack" support (See percenthack)
- UUCP hook
5.8. SMTP delivery
- RFC 82 RFC 974, and RFC 23 compliant
- 8-bit clean
- Automatic downed host backoffs
- Artificial routing--smarthost, localnet, mailertable (See smtproutes)
- per-buffer timeouts
- Passive SMTP queue--perfect for SLIP/PPP (via serialmail)
- AutoTURN support (via serialmail)
5.9. Forwarding and mailing lists
- Hashed forwarding databases (via fastforward)
- Address wildcards (See .qmail-default)
- 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
- RFC 39 compliant
- UIDL support
- TOP support
- APOP hook
- modular password checking (via checkpassword)
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.
- daemontools--a set of tools for managing daemons and their logs
- qmailanalog--a set of qmail log file analysis tools
- serialmail--tools for mailing over slow networks
- 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.
Other
packages by Dan Bernstein, such as daemontools and ucspi-tcp,
are copyrighted by the author, and are not distributed with a
statement of user's rights. Inhttp://cr.yp.to/softwarelaw.html,
he outlines what he thinks your rights are under U.S. copyright law.
See also http://en.wikipedia.org/wiki/License-free_software.
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.
Jonathan
de Boyne Pollard has reviews of many Unix MTAs
at http://homepages.tesco.net/~J.deBoynePollard/Reviews/UnixMTSes/.
Another detailed comparison is available
at http://www.geocities.com/mailsoftware42/.
. 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:
- /var/qmail/doc/FAQ, the plain text version, and
- The web FAQ at http://cr.yp.to/qmail/faq.html.
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.
For
more information, see http://www.apress.com/catalog/book/935402/.
To order this book from my bookstore, in association with Amazon.com,
seehttp://www.amazon.com/exec/obidos/ASIN/935402/davesill.
.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.
To
order this book from my bookstore, in association with Amazon.com,
see http://www.amazon.com/exec/obidos/ASIN/4750/davesill.
.4.3. qmail
John
Levine has written a qmail book
for O'Reilly & Associates (http://www.oreilly.com/).
See http://qmail.gurus.com/ for
more info including the Table of Contents and a sample chapter.
To
order this book from my bookstore, in association with Amazon.com,
see http://www.amazon.com/exec/obidos/ASIN/65926285/davesill.
.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.
For
more information or to order this book,
see http://www.amazon.com/exec/obidos/ASIN/06723454/davesill.
.4.5. qmail: Yuksek Performansli E-Posta Sunucu
Ismail
Yenigul, et al, have written a Turkish-language qmail book.
See http://www.acikakademi.com/catalog/qmail/.
.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.
- http://www.flounder.net/qmail/qmail-howto.html: Adam McKenna's HOWTO.
. 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:
- listname-subscribe-joe=example.com@list.cr.yp.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
See http://www.qmail.org/top.html#paidsup for
a list of commercial support providers.
.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
