Linux Email Second Edition - McDonald, Alistair Pszów

Many businesses want to run their email servers on Linux for greater control and flexibility of corporate communications, but getting started can be complicated. The attractiveness of a free-to-use and robust email service running on Linux can be undermined by the apparent technical challenges involved. Some of the complexity arises from the fact that an email server consists of several components that must be installed and configured separately, then integrated together.This book gives you just what you need to know to set up and maintain an email server. Unlike other approaches that deal with one component at a time, this book delivers a step-by-step approach across all the server components, leaving you with a complete working email server for your small business network.Starting with a discussion on why you should even consider hosting your own email server, the book covers setting up the mail server. We then move on to look at providing web access, so that users can access their email out of the office. After this we look at the features you'll want to add to improve email productivity: virus protection, spam detection, and automatic email processing. Finally we look at an essential maintenance task: backups.Written by professional Linux administrators, the book is aimed at technically confident users and new and part-time system administrators. The emphasis is on simple, practical and reliable guidance.Based entirely on free, Open Source software, this book will show you how to set up and manage your email server easily. Spis treści: 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 Postfixs 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