Exim

Exim delivers electronic mail, both local and remote. It has all the virtues of a good postman: it's easy to talk to, reliable, efficient, and eager to accommodate even the most complex special requests. It's the default mail transport agent installed on some Linux systems, runs on many versions of Unix, and is suitable for any TCP/IP network with any combination of hosts and end-user mail software.

Exim is growing in popularity because it is open source, scalable, and rich in features such as the following:

• Compatibility with the calling interfaces and options of Sendmail (for which Exim is usually a drop-in replacement)
• Lookups in LDAP servers, MySQL and PostgreSQL databases, and NIS or NIS+ services
• Support for many kinds of address parsing, including regular expressions that are compatible with Perl 5
• Sophisticated error handling
• Innumerable tuning parameters for improving performance and handling enormous volumes of mail

Best of all, Exim is easy to configure. You never have to deal with ruleset 3 or worry that a misplaced asterisk will cause an inadvertent mail bomb.

While a basic configuration is easy to read and can be created quickly, Exim's syntax and behavior do get more subtle as you enter complicated areas like virtual hosting, filtering, and automatic replies. This book is a comprehensive survey that provides quick information for people in a hurry as well as thorough coverage of more advanced material.

Preface

Chapter 1. Introduction

Chapter 2. How Internet Mail Works
   Different Types of MTA
   Internet Message Standards
   RFC 822 Message Format
   The Message ``On the Wire'
   Summary of the SMTP Protocol
   Forgery
   Authentication and Encryption
   Routing a Message
   Checking Incoming Mail
   Overview of the DNS
   DNS Records Used for Mail Routing
   Related DNS Records
   Common DNS Errors
   Role of the Postmaster

Chapter 3. Exim Overview
   Exim Philosophy
   Exim's Queue
   Receiving and Delivering Messages
   Exim Processes
   Coordination Between Processes
   How Exim Is Configured
   How Exim Delivers Messages
   Local and Remote Addresses
   Processing an Address
   A Simple Example
   Complications While Directing and Routing
   Complications During Delivery
   Complications After Delivery
   Use of Transports by Directors and Routers

Chapter 4. Exim Operations Overview
   How Exim Identifies Messages
   Watching Exim at Work
   The Runtime Configuration File
   The Default Qualification Domain
   Handling Frozen Bounce Messages
   Reducing Activity at High Load
   Limiting Message Sizes
   Parallel Remote Delivery
   Controlling the Number of Delivery Processes
   Large Message Queues
   Large Installations

Chapter 5. Extending the Delivery Configuration
   Multiple Local Domains
   Virtual Domains
   Mailing Lists
   Using an External Local Delivery Agent
   Multiple User Addresses
   Mixed Local/Remote Domains
   Delivering to UUCP
   Ignoring the Local Part in Local Deliveries
   Handling Local Parts in a Case-Sensitive Manner
   Scanning Messages for Viruses
   Modifying Message Bodies

Chapter 6. Options Common to Directors and Routers
   Conditional Running of Routers and Directors
   Changing a Driver's Successful Outcome
   Adding Data for Use by Transports
   Debugging Directors and Routers
   Summary of Director/Router Generic Options

Chapter 7. The Directors
   Conditional Running of Directors
   Optimizing Single-Level Aliasing
   Adding Data for Use by Transports
   The aliasfile and forwardfile Directors
   The aliasfile Director
   The forwardfile Director
   The localuser Director
   The smartuser Director

Chapter 8. The Routers
   Timeouts While Routing
   Domains That Route to the Local Host
   The lookuphost Router
   The domainlist Router
   The ipliteral Router
   The queryprogram Router

Chapter 9. The Transports
   Options Common to All Transports
   The smtp Transport
   Environment for Local Transports
   Options Common to the appendfile and pipe Transports
   The appendfile Transport
   The pipe Transport
   The lmtp Transport
   The autoreply Transport

Chapter 10. Message Filtering
   Examples of Filter Commands
   Filtering Compared with an External Delivery Agent
   Setting Up a User Filter
   Setting Up a System Filter
   Testing Filter Files
   Format of Filter Files
   Significant Actions
   Filter Commands
   The add Command
   Delivery Commands
   Mail Commands
   Logging Commands
   The testprint Command
   The finish Command
   Obeying Filter Commands Conditionally
   Additional Features for System Filters

Chapter 11. Shared Data and Exim Processes
   Message Files
   Locking Message Files
   Hints Files
   Log Files
   User and Group IDs for Exim Processes
   Process Relationships
   The Daemon Process
   Reception Processes
   Queue Runner Processes
   Delivery Processes
   Summary of Message Handling Process Types
   Other Types of Process

Chapter 12. Delivery Errors and Retrying
   Retrying After Errors
   Remote Delivery Errors
   Local Delivery Errors
   Routing and Directing Errors
   Retry Rules
   Computing Retry Times
   Using Retry Times
   Retry Rule Examples
   Timeout of Retry Data
   Long-Term Failures
   Ultimate Address Timeout
   Intermittently Connected Hosts

Chapter 13. Message Reception and Policy Controls
   Message Sources
   Message Size Control
   Messages from Local Processes
   Unqualified Addresses from Remote Hosts
   Checking a Remote Host
   Checking Remote Sender Addresses
   Checking Recipient Addresses
   Checking Header Line Syntax
   Relay Control
   Customizing Prohibition Messages
   Incoming Message Processing

Chapter 14. Rewriting Addresses
   Automatic Rewriting
   Configured Rewriting
   Rewriting Rules
   Rewriting Patterns
   Rewriting Flags
   A Further Rewriting Example
   Testing Rewriting Rules

Chapter 15. Authentication, Encryption, and Other SMTP Processing
   SMTP Authentication
   Encrypted SMTP Connections
   SMTP over TCP/IP
   Local SMTP
   Batched SMTP

Chapter 16. File and Database Lookups
   Single-Key Lookup Types
   Query-Style Lookup Types
   Quoting Lookup Data
   NIS+
   LDAP
   MySQL and PostgreSQL
   DNS Lookups
   Implicit Keys in Query-Style Lookups
   Temporary Errors in Lookups
   Default Values in Single-Key Lookups
   Partial Matching in Single-Key Lookups
   Lookup Caching

Chapter 17. String Expansion
   Variable Substitution
   Header Insertion
   Operations on Substrings
   Character Translation
   Text Substitution
   Conditional Expansion
   Lookups in Expansion Strings
   Extracting Fields from Substrings
   IP Address Masking
   Quoting
   Reexpansion
   Running Embedded Perl
   Testing String Expansions

Chapter 18. Domain, Host, and Address Lists
   Negative Items in Lists
   List Items in Files
   Lookup Items in Lists
   Domain Lists
   Host Lists
   Address Lists

Chapter 19. Miscellany
   Security Issues
   Privileged Users
   RFC Conformance
   Timestamps
   Checking Spool Space
   Control of DNS Lookups
   Bounce Message Handling
   Miscellaneous Controls

Chapter 20. Command-Line Interface to Exim
   Input Mode Control
   Additional Message Data
   Immediate Delivery Control
   Error Routing
   Queue Runner Processes
   Configuration Overrides
   Watching Exim's Queue
   Message Control
   Testing Options
   Options for Debugging
   Terminating the Options
   Embedded Perl Options
   Compatibility with Sendmail
   Calling Exim by Different Names

Chapter 21. Administering Exim
   Log Files
   Log Destination Control
   Format of Main Log Entries
   Cycling Log Files
   Extracting Information from Log Files
   Watching What Exim is Doing
   The Exim Monitor
   Maintaining Alias and Other Datafiles
   Hints Database Maintenance
   Mailbox Maintenance

Chapter 22. Building and Installing Exim
   Prerequisites
   Fetching and Unpacking the Source
   Configuration for Building
   The Building Process
   Installing Exim
   Testing Before Turning On
   Turning Exim On
   Installing Documentation in Info Format
   Upgrading to a New Release

Appendix A. Summary of String Expansion

Appendix B. Regular Expressions

Index