The Sendmail program is one of the most widely used Internet Mail Transport Agents -MTAs in the world. The purpose of an MTA is to send mail from one machine to another, and nothing
else. Sendmail is not a client program, which you use to read your e-mail. Instead, it actually moves your email over networks, or the Internet, to where you want it to go. Sendmail has been an easy target for system
crackers to exploit in the past, but with the advent of Sendmail version 8, this has become much more difficult.