Usually this program is sendmail or smail running in the background. Turn it off or change the command line options in /etc/rc.conf
(or, prior to FreeBSD 2.2.2, /etc/sysconfig). It is best to leave it on, unless you have a specific reason to want it off. Example: You are building a
Firewall.
You should be aware that sendmail is a potential weak link in a secure site. Some versions of sendmail have known security problems.
sendmail does two jobs. It looks after delivering and receiving mail.
If sendmail needs to deliver mail off your site it will look up in the DNS to determine the actual host that will receive mail for the destination.
If it is acting as a delivery agent sendmail will take the message from the local queue and deliver it across the Internet to another sendmail on the receivers computer.