Linux Email电子书

Linux E-mail

Table of Contents

Linux E-mail

Credits

About the Authors

About the Reviewers

Preface

What this book covers

Who this book is for

Conventions

Reader feedback

Customer support

Errata

Piracy

Questions

1. Linux and E-mail Basics

Why manage your own e-mail server

What you need to host an e-mail server

Sizing the hardware of your e-mail server

Main e-mail protocols: SMTP, POP, and IMAP

Overview

POP protocol

IMAP protocol

The SMTP protocol

E-mail and DNS

DNS record types used by e-mail applications

Backup mail servers

Summary

2. Setting up Postfix

Introduction to Postfix

What is Postfix

Postfix architecture: An overview

New message arrival

Scheduling message deliveries

Message delivery

Supporting programs

Installation and basic configuration

Choosing the Postfix version

Installing from a package

Installing from source code

The Postfix configuration

main.cf

master.cf

Lookup tables

Getting Postfix up and running

Domains and hostnames

Indirect mail delivery through your ISP

Choosing network interfaces

Choosing mailbox format for local deliveries

Error reporting

Other useful configuration parameters

Starting Postfix and sending the first message

Stopping spam and other unwanted messages

Postfix's anti-spam methods: An overview

Understanding SMTP restrictions

Access maps

Access map examples

Implementing new policies

Using DNS blacklists

Choosing DNS blacklists

Stopping messages based on content

Configuring header and body checks

Header and body checks examples

Caveats

Virtual alias domains and local aliases

Virtual alias domains

Many virtual alias domains mapping to one local domain

One virtual alias domain mapping to many local domains

Group addresses

Introducing MySQL lookups

Local aliases

Command deliveries

Common pitfalls

Other address rewriting mechanisms

Troubleshooting Postfix problems

Reading and interpreting the log files

Message queue ID

SMTP submission and local delivery

Local submission and SMTP delivery

Connection problems upon SMTP delivery

Getting more detailed log messages

Troubleshooting lookup tables with Postmap

Getting help from the Postfix mailing list

Summary

3. Incoming Mail with POP and IMAP

Choosing between POP and IMAP

Downloading and installing Courier-IMAP

Installing Courier-IMAP from a distribution repository

Installing Courier-IMAP from RPM

Installing Courier-IMAP using the Debian package format

Installing Courier-IMAP from source

Prerequisites

Building the Courier Authentication Library

Configuring the Courier Authentication Library

Resolving errors

Building Courier-IMAP

Handling errors

Using POP3

Configuring Courier-IMAP for POP3

Testing the POP3 Service

Retrieving E-mail via POP3 with Windows Live Mail

Using IMAP

Configuring Courier for IMAP

Testing the IMAP service

Retrieving mail via IMAP with Mozilla Thunderbird

Summary

4. Providing Webmail Access

The webmail solution

The benefits

Easy and quick access

Easy remote access

No need to maintain clients

Configuring mail server interface via the user interface

Possible security benefits

The disadvantages

Performance

Compatibility with large e-mail volumes

Compatibility with e-mail attachments

Security issues

The SquirrelMail webmail package

SquirrelMail installation and configuration

Prerequisites to installation

Basic requirements

Installing Apache2

PHP

Perl

Review configuration

Installing SquirrelMail

Source installation

Configuring SquirrelMail

SquirrelMail plugins

Installing plugins

Example plugin installation

Downloading and unpacking the plugin

Performing custom installation

Enabling the plugin in conf.pl

Useful plugins

Securing SquirrelMail

Summary

5. Securing Your Installation

Configuring Postfix network maps

SMTP-after-POP

Virtual Private Networks

SMTP Authentication

Static IP ranges

Generic relay rules

Explicit relay rules

Dynamic IP ranges

Cyrus SASL

SASL layers

Authentication interface

Mechanism

Method

Password verification service

Installing Cyrus SASL

Configuring Cyrus SASL

Selecting a password verification service

Choosing a log level

Choosing valid mechanisms

saslauthd

Using an IMAP server as authentication backend

Using an LDAP server as authentication backend

Using the local user accounts

Using PAM

auxprop

Configuring the sasldb plugin

Configuring the sql plugin

authdaemond

Setting the authdaemond password verification service

Configuring the authdaemond socket path

Testing Cyrus SASL authentication

Configuring Postfix SMTP AUTH

Preparing the configuration

Enabling SMTP AUTH

Setting the security policy

Including broken clients

Testing SMTP AUTH

Enabling relaying for authenticated clients

Securing plaintext mechanisms

Enabling Transport Layer Security

Configuring security policy

Dictionary attacks

Recipient maps

Checking local domain recipients

Checking relay domain recipients

Rate-limiting connections

Summary

6. Getting Started with Procmail

Introduction to Procmail

Who wrote it and when

How can a filtering system help me?

Potential uses of mail filtering

Filtering and sorting mail

Forwarding mail

Processing the mail in an application

Acknowledgements and out of office/vacation replies

File locking and integrity

What Procmail is not suitable for

Downloading and installing Procmail

Installing via a package manager

Installing from source

Installation options/considerations

Individual installation

System-wide installation

Integration with Postfix for system-wide delivery

Creating an alias for system accounts

Adding Procmail to the Postfix configuration

Postfix-provided environment variables

Basic operations

Configuration file

File format

Configuration file dissection

Analyzing a simple rule

The rule structure

Variable analysis

Rule analysis

Creating and testing a rule

A "hello world" example

Creating rc.testing

Performing static testing of the script

Configuring Procmail to process rc.testing

Testing the setup

Configuration debugging

Checking for typos in the scripts

Looking at the log file for error messages

Checking file and directory permissions

Turning on Full Logging

Taking steps to avoid disasters

Understanding e-mail structure

Message body

E-mail headers

Header structure

Official definitions for headers

Example rule sets

From header

Return-Path Header

Filtering by Return-Path

To and Cc headers

Filtering by To or Cc

Subject header

Filtering by subject

System-wide rules

Removing executables

Large e-mails

Summary

7. Advanced Procmail

Delivering and non-delivering recipes

Non-delivering example

Formail

Advanced recipe analysis

Adding comments

Assigning variables

Performing substitutions

Assigning variable with default values

Assigning command output to variables

Pseudo-variables

Mailbox variables

Program variables

System interaction variables

Logging variables

Procmail's state variables

Message content variables

Locking variables

Error-handling variables

Miscellaneous variables

Printing Procmail variables

Recipes

Colon line

Locking

Automatic locking

Enforced locking

No locking

Flags

Default flags

Scope of matching: HB

Scope of action: hb

Flow control: aAeEc

Case sensitivity: D

Execution mode: fwWir

Conditions

Applying a rule unconditionally

Tests with regular expressions

Testing the size of a message part

Testing the exit code of an external program

Negation

Variable substitution in conditions

Action line

Forwarding to other addresses

Feeding to a shell or command pipeline

Saving to a folder

Compound recipes

Regular expressions

Introduction to regular expressions

The dot

Quantifier operation

The asterisk

The plus sign

Restrictive matches using parentheses

Creating a simple spam filter

Character classes

Start of line

End of Line

Further reading

^TO and ^TO_

^FROM_MAILER

^FROM_DAEMON

Advanced recipes

Creating a vacation auto reply

Organizing mail by date

Informing users about large mail

Procmail Module Library

Putting it all together

Creating a structure to base your own rules upon

Rc.system

Rc.lists

Rc.killspam

Rc.vacation

Rc.largefiles

Rc.viruses

Rc.spamfilter

Summary

8. Busting Spam with SpamAssassin

Why filter e-mail

Spam is a moving target

Spam filtering options

Introduction to SpamAssassin

Downloading and installing SpamAssassin

Using CPAN

Configuring CPAN

Installing SpamAssassin using CPAN

Using the rpmbuild utility

Using pre-built RPMs

Testing the installation

Modified e-mails

Using SpamAssassin

Using SpamAssassin with Procmail

Global procmailrc file

Using SpamAssassin on a per-user basis

Using SpamAssassin as a daemon with Postfix

Using SpamAssassin with amavisd-new

Installing amavisd-new from package

Installation prerequisites

Installing from source

Creating a user account for amavisd-new

Configuring amavisd-new

Configuring Postfix to run amavisd-new

Configuring e-mail clients

Microsoft Outlook

Microsoft Outlook Express

Mozilla Thunderbird

Customizing SpamAssassin

Reasons to customize

Rules and scores

Altering rule scores

Using other rulesets

Whitelists and blacklists

Bayesian filtering

Other SpamAssassin features

Summary

9. Antivirus Protection

Introduction to ClamAV

Document types supported

Downloading and installing ClamAV

Adding a new system user and group

Installing from a package

Installing from source code

Requirements

Building and installing

Quick test

Editing the config files

clamd

Examining the sample config file

freshclam

Closest mirrors

Examining the sample config file

File permissions

Post installation testing

EICAR test virus

Testing clamscan

Testing clamd

Testing freshclam

Introduction to ClamSMTP

Building and installing

Configuring into Postfix

Configuring clamSMTP

Examining the sample config file

Testing e-mail filtering

Testing mail-borne virus filtering

Thorough e-mail-borne testing

Automating update of virus data

Setting up auto updating

Automating startup and shutdown

ClamSMTP

ClamAV

Monitoring log files

Disinfecting files

Summary

10. Backing Up Your System

Backup options

RAID

Image backups

File system backups

Ad hoc backups

What to back up

System inventory

Obtaining a list of installed software

System configuration files

Authentication data

The users' mailboxes

Log files

The mail queue

What not to back up

Backing up users' e-mail

Mail storage

Using dump

Full dump

Incremental dumps

Using restore

Interactive restore

Non-interactive restore across the network

Backing up configurations and logs

Transferring configurations and logs to backup media

Restoring the configuration

Automating backups

Backup script

Adding crontab entries

Verifying restoration procedures

Summary

Index