Sendmail

Elandsys.com: Sendmail
Features a tutorial on how to install and configure it.
http://www.elandsys.com/resources/sendmail/

Explosion in a Punctuation Factory
Excellent tutorial on how sendmail's rewriting rules work. Written by Brian Costales, the author of the best sendmail book around, "Sendmail", published by O'Reilly and Associates.
http://www.networkcomputing.com/unixworld/tutorial/01/01.txt.html

A First Guide for E-mail Installation
A draft about the installation/configuration of sendmail.
http://www.sendmail.org/~ca/email/setup1.html

HP-UX Mailing Services Administrator's Guide
HP-UX sendmail documentation. Also applicable to sendmail in general.
http://docs.hp.com/en/5991-6611/index.html

Jeremy Mates’s sendmail pages
Sendmail flow diagram with explanations and example configuration files for various situations.
http://sial.org/howto/sendmail/

Linux-Sec.net
Features minimum mail server hardening recommendations. Includes information on how to do it, antispam, filtering, open relay, antivirus, and statistics analyzer.
http://www.linux-sec.net/Mail/

MeTA1
MeTA1 is a successor of Sendmail X. Release notes, documentation, source code and contact information.
http://www.meta1.org/

Sendmail FAQ
Frequently asked questions about sendmail.
http://www.sendmail.org/faq/

Sendmail Inc.
Commercial Sendmail products and services.
http://www.sendmail.com/

Sendmail Routing with LDAP
Step-by-step instructions on using sendmail's LDAP routing feature. [Sun support contract required]
http://sunsolve.sun.com/search/document.do?assetkey=1-9-75062-1

Sendmail: Theory and Practice
Homepage for the sedmail book by Paul A. Vixie and Frederick M. Avolio. Errata, sample chapter and ordering information.
http://smtap.al.org/

Sendmail V8: A (Smoother) Engine Powers Network E-mail
Article on sendmail version 8 features. Mostly of historical value.
http://www.networkcomputing.com/unixworld/tutorial/008/008.txt.html

Tek-Tips Sendmail Forum
Technical support forums and mutual help system for computer professionals. Selling and recruiting forbidden.
http://www.tek-tips.com/threadminder.cfm?pid=14