This quick-reference guide to the sendmail program provides a complete overview of sendmail, from command-line switches to configuration commands, from options declarations to macro definitions, and from m4 features to debugging switches -- all packed into a convenient, carry-around booklet. sendmail is the program that acts like a traffic cop in routing and delivering mail on UNIX-based networks -- it is a Mail Transport Agent (MTA), accepting mail from Mail User Agents (MUAs), mail users (humans), and other MTAs. Then, it delivers that mail to Mail Delivery Agents (MDAs) on the local machine, or transports that mail to another MTA on another machine. Although sendmail is used on almost every UNIX system, it's one of the last great uncharted territories -- and most difficult utilities to learn -- in UNIX system administration. Designed as a companion volume to sendmail, 2nd Edition, this guide covers the latest version (V8.8) from the University of California, Berkeley, and has extensive cross-references to sections in the main volume. Both books are coauthored by Eric Allman, the creator of sendmail.