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Postfix
The Definitive Guide
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Postfix
The Definitive Guide
Kyle D. Dent
Beijing
•
Cambridge
•
Farnham
•
Köln
•
Sebastopol
•
Tokyo
,psfx.book.2768 Page iii Thursday, March 24, 2011 1:20 PM
www.it-ebooks.info
Postfix: The Definitive Guide
by Kyle D. Dent
Copyright © 2004 O’Reilly Media, Inc. All rights reserved.
Printed in the United States of America.
Published by O’Reilly Media, Inc., 1005 Gravenstein Highway North, Sebastopol, CA 95472.
O’Reilly Media, Inc. books may be purchased for educational, business, or sales promotional use. On-
line editions are also available for most titles (safari.oreilly.com). For more information, contact our cor-
porate/institutional sales department: (800) 998-9938 or corporate@oreilly.com.
Editor:
Andy Oram
Production Editor:
Reg Aubry
Cover Designer:
Ellie Volckhausen
Interior Designer:
David Futato
Printing History:
December 2003: First Edition.
Nutshell Handbook, the Nutshell Handbook logo, and the O’Reilly logo are registered trademarks of
O’Reilly Media, Inc. Postfix: The Definitive Guide, the image of a dove, and related trade dress are
trademarks of O’Reilly Media, Inc. Many of the designations used by manufacturers and sellers to
distinguish their products are claimed as trademarks. Where those designations appear in this book,
and O’Reilly Media, Inc. was aware of a trademark claim, the designations have been printed in caps or
initial caps.
While every precaution has been taken in the preparation of this book, the publisher and author assume
no responsibility for errors or omissions, or for damages resulting from the use of the information
contained herein.
ISBN: 978-0-596-00212-1
[LSI] [2011-03-25]
,psfx.book.2768 Page iv Thursday, March 24, 2011 1:20 PM
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v
Table of Contents
Foreword
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ix
Preface
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
xi
1. Introduction
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1
Postfix Origins and Philosophy 1
Email and the Internet 3
The Role of Postfix 5
Postfix Security 6
Additional Information and How to Obtain Postfix 8
2. Prerequisites
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10
Unix Topics 10
Email Topics 12
3. Postfix Architecture
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
19
Postfix Components 19
How Messages Enter the Postfix System 20
The Postfix Queue 22
Mail Delivery 22
Tracing a Message Through Postfix 25
4. General Configuration and Administration
. . . . . . . . . . . . . . . . . . . . . . . . . . . .
28
Starting Postfix the First Time 29
Configuration Files 30
Important Configuration Considerations 41
Administration 44
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vi | Table of Contents
master.cf 47
Receiving Limits 51
Rewriting Addresses 52
chroot 56
Documentation 57
5. Queue Management
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
58
How qmgr Works 58
Queue Tools 62
6. Email and DNS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
68
DNS Overview 68
Email Routing 69
Postfix and DNS 72
Common Problems 75
7. Local Delivery and POP/IMAP
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
77
Postfix Delivery Transports 77
Message Store Formats 78
Local Delivery 80
POP and IMAP 83
Local Mail Transfer Protocol 84
8. Hosting Multiple Domains
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
89
Shared Domains with System Accounts 90
Separate Domains with System Accounts 90
Separate Domains with Virtual Accounts 91
Separate Message Store 95
Delivery to Commands 95
9. Mail Relaying
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
103
Backup MX 103
Transport Maps 106
Inbound Mail Gateway 109
Outbound Mail Relay 110
UUCP, Fax, and Other Deliveries 111
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Table of Contents | vii
10. Mailing Lists
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
112
Simple Mailing Lists 113
Mailing-List Managers 117
11. Blocking Unsolicited Bulk Email
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
125
The Nature of Spam 125
The Problem of Spam 126
Open Relays 127
Spam Detection 127
Anti-Spam Actions 129
Postfix Configuration 130
Client-Detection Rules 131
Strict Syntax Parameters 143
Content-Checking 144
Customized Restriction Classes 147
Postfix Anti-Spam Example 149
12. SASL Authentication
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
151
SASL Overview 152
Postfix and SASL 154
Configuring Postfix for SASL 154
Testing Your Authentication Configuration 159
SMTP Client Authentication 162
13. Transport Layer Security
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
164
Postfix and TLS 165
TLS Certificates 165
14. Content Filtering
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
174
Command-Based Filtering 175
Daemon-Based Filtering 177
Other Considerations 181
15. External Databases
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
183
MySQL 184
LDAP 190
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viii | Table of Contents
A. Configuration Parameters
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
195
B. Postfix Commands
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
219
C. Compiling and Installing Postfix
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
221
D. Frequently Asked Questions
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
234
Index
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
239
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[...]... (space or tab characters) to show that they are continuations of the previous line The standard document provides a lot of detail about the header fields and what they should be used for There are rules about how fields relate to each other and when one or another must be used, but in the simplest case, the only required fields are the Date: and the From: fields The standard also provides for customized... level Status 2xx The requested action was successful The client may continue to the next step 3xx Command was accepted, but the server expects additional information The client should send another command with the additional information 4xx The command was not successful, but the problem is temporary The client should retry the action at a later time 5xx The command was not successful, and the problem is... address as the envelope destination address, but this is not required nor is it always the case From the MTA’s point of view, message headers are part of the content of an email message The delivery of a message is determined by the addresses specified during the SMTP conversation These addresses are the envelope addresses, and they are the only thing that determine where messages go See The SMTP Protocol”... permanent The client should not retry the action After receiving the welcome banner, introduce yourself with the HELO command The hostname after the HELO command should be the name of the system you’re connecting from: HELO mail.oreilly.com The server replies with a success So you may continue: 250 mail.oreilly.com Indicate who the message is from with the MAIL FROM command: MAIL FROM: The. .. for email The term message store applies to persistent message storage regardless of how or where it is kept Once the message has been placed in the message store, it stays there until the intended recipient is ready to pick it up The recipient uses an MUA to retrieve the message and read it The MUA contacts the server that provides access to the message store This server is separate from the MTA that... determines during the SMTP conversation (see The SMTP Protocol” later in the chapter) that it will not accept the message, it rejects the message At that point the sending system should generate an error report to deliver to the original sender Sometimes the MTA accepts a message and later discovers that it cannot be delivered—perhaps the intended recipient doesn’t exist or there is a problem in the final... message flow Email and the Internet This is the Title of the Book, eMatter Edition www.it-ebooks.info Copyright © 2007 O’Reilly & Associates, Inc All rights reserved | 3 Ultimately, a message arrives at the MTA that is the final destination If the message is destined for a user on the system, the MTA passes it to a message delivery agent (MDA) for the final delivery The MDA might store the message as a plain... FROM: The server accepts the sending address: 250 Ok Indicate who the message is to with the RCPT TO command: RCPT TO: The server accepts the recipient address: 250 Ok Now you are ready to send the content of the message The DATA command tells the server that you have an RFC 2822 message ready to transfer: DATA The server replies that it accepts the command and is expecting you... specification describes the format for transmission, but many implementations use the same or a similar format to store messages A message is comprised of two parts: the header and the body The header contains specific fields with names such as To, From, or Subject followed by a colon (:) After the colon comes the contents of the field One message 14 | Chapter 2: Prerequisites This is the Title of the Book, eMatter... another MTA to relay or deliver a message Originally, SMTP had no means to authenticate users, but extensions to the protocol provide the capability, if required See Chapter 7 for more information on authenticating SMTP users POP/IMAP and mailbox access When users want to retrieve their messages, they use their MUA to connect to a POP or IMAP server to retrieve them POP users generally take all their . Network Administration Running Mac OS X Panther Mac OS X Panther for Unix Geeks Mac OS X Panther in a Nutshell Mac OS X Panther Pocket Guide Learning Unix for Mac OS X Panther Applescript: The Definitive Guide networking.oreilly.com networking.oreilly.com. of seconds. Read the books on your Bookshelf from cover to cover or simply flip to the page you need. Try it today with a free trial. www.it-ebooks.info Postfix The Definitive Guide Kyle D. Dent Beijing • Cambridge • Farnham • Köln • Sebastopol • Tokyo ,psfx.book.2768. First Edition. Nutshell Handbook, the Nutshell Handbook logo, and the O’Reilly logo are registered trademarks of O’Reilly Media, Inc. Postfix: The Definitive Guide, the image of a dove, and related
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