The sendmail program is a Mail Transport Agent (MTA). It accepts mail from Mail User Agents (MUAs), mail users (humans), and other MTAs. It then delivers that mail to Mail Delivery Agents (MDAs) on the local machine, or transports that mail to another MTA at another machine. The behavior of sendmail is determined by its command line and by commands in its configuration file.
The sendmail program is written and maintained by Eric Allman at sendmail.org. Versions V8.7 and earlier are no longer supported and are no longer considered secure. If you are not currently running V8.8, we recommend you upgrade now. This Desktop Reference covers sendmail version 8.8.5.
This Desktop Reference is a companion to the second edition of the sendmail book by Bryan Costales with Eric Allman, published by O'Reilly & Associates. Section numbers herein reference the section numbers in that book. This is a reference guide only - for detail or tutorial information, refer to the full sendmail book.