After building websites for over 15 years, I have found myself using Drupal more and more for almost all of the sites built for...
An open source mail delivery system that ships with many versions of Linux. In simple terms... it delivers and receives email. Sendmail is very powerful and handy to anyone running their own server. Chances are... if you are on shared hosting, you will probably not have to deal with sendmail. If you are running a VPS or dedicated web server, using and configuring sendmail may be an issue.