Many users initially find email programs difficult to configure, primarily due to the large number of options available. Access to additional documentation can be very helpful, especially when setting sensitive configuration options.
Information about how to configure Sendmail is included with the sendmail and sendmail-cf packages.
/usr/share/doc/sendmail/README.cf — Contains information on m4, file locations for Sendmail, supported mailers, how to access enhanced features, and much more.
/usr/share/doc/sendmail/README — Contains information on the Sendmail directory structure, IDENT protocol support, details on directory permissions, and the common problems these permissions can cause if misconfigured.
In addition, the sendmail and aliases man pages contain helpful information covering various Sendmail options and the proper configuration of the Sendmail /etc/mail/aliases file, respectively.
/usr/share/doc/fetchmail-<version-number> — Contains a full list of Fetchmail features in the FEATURES file and an introductory FAQ document.
/usr/share/doc/procmail-<version-number> — Contains a README file that provides an overview of Procmail, a FEATURES file that explores every program feature, and an FAQ file with answers to many common configuration questions.
When learning how Procmail works and creating new recipes, these Procmail man pages are invaluable:
procmail — Provides an overview of how Procmail works and the steps involved with filtering email.
procmailrc — Explains the rc file format used to construct recipes.
procmailex — Gives a number of useful, real-world examples of Procmail recipes.
procmailsc — Explains the weighted scoring technique used by Procmail to see if a particular recipe matches a certain message.
http://www.redhat.com/mirrors/LDP/HOWTO/Mail-Administrator-HOWTO.html — Provides an overview of how email works and examines possible email solutions and configurations on the client and server sides.
http://www.redhat.com/mirrors/LDP/HOWTO/Mail-User-HOWTO — Looks at email from the user's perspective, investigates various popular email client applications, and gives an introduction to topics such as aliases, forwarding, auto-replying, mailing lists, mail filters, and spam.
http://www.redhat.com/mirrors/LDP/HOWTO/mini/Secure-POP+SSH.html — Demonstrates a way to retrieve POP email using SSH with port forwarding, so that your email passwords and messages will be transferred securely.
http://www.sendmail.net — Contains news, interviews, and articles concerning Sendmail, including an expanded view of the many options available.
http://www.sendmail.org — Offers a thorough technical breakdown of Sendmail features and configuration examples.
http://tuxedo.org/~esr/fetchmail — The home page for Fetchmail, featuring an online manual and thorough FAQ.
http://www.procmail.org — The home page for Procmail, with links to assorted mailing lists dedicated to Procmail as well as various FAQ documents.
http://www.ling.helsinki.fi/users/reriksso/procmail/mini-faq.html — An excellent Procmail FAQ, with troubleshooting tips and details about file locking and the use of wildcard characters.
http://www.uwasa.fi/~ts/info/proctips.html — Points out dozens of tips that make using Procmail in various situations much easier, including how to test .procmailrc files and use Procmail scoring to decide if a particular action should be taken.
Sendmail by Bryan Costales with Eric Allman et al; O'Reilly & Associates — A good Sendmail reference written with the assistance of the original creator of Delivermail and Sendmail.
Removing the Spam: Email Processing and Filtering by Geoff Mulligan; Addison-Wesley Publishing Company — A volume that looks at various methods used by email administrators that use established tools, such as Sendmail and Procmail, to manage spam problems.
Internet Email Protocols: A Developer's Guide by Kevin Johnson; Addison-Wesley Publishing Company — Provides a very thorough review of major email protocols and the security they provide.
Managing IMAP by Dianna Mullet and Kevin Mullet; O'Reilly & Associates — Details the steps required to configure an IMAP server.