Wednesday, February 24, 2016

Life with qmail - document

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

  • RFC 822 and RFC 23 compliant
  • 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)
  • User masquerading (See MAILUSER and MAILHOST)
  • Automatic Mail-Followup-To creation (See QMAILMFTFILE)

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
  • 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

5.8. SMTP delivery

5.9. Forwarding and mailing lists

  • Sendmail .forward compatibility (via dot-forward)
  • Hashed forwarding databases (via fastforward)
  • Sendmail /etc/aliases compatibility (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.
  • dot-forward--a Sendmail .forward file compatibility add-on
  • fastforward--a Sendmail alias database compatibility add-on
  • ucspi-tcp--an inetd replacement
  • 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:
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

. 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


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Location: Chennai, Tamil Nadu, India

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