Sending Mail from Linux servers

there are many different mail programs you can use, but the simplest is to type

%mail person@example.com

from the command line, using ^D to end the message.

Of course, you have to make sure that your linux machine doesn't have any blocked ports, has sendmail running, is associated with a DNS so that others can find you, has a trusted site that it can relay mail from, etc, etc.

here is a tutorial on setting up sendmail: http://computernetworkingnotes.com/network-administrations/sendmail-server.html

You could use sendmail,,,,

In /etc/mail/sendmail.mc file contains following line:
dnl define(`SMART_HOST',`smtp.your.provider')

Replace "smtp.your.provider" with the fully qualified domain name to look like this:
define(`SMART_HOST',`my.relay.server')

Then restart
# service sendmail restart

Is the machine already setup to send email?  

There is a lot that goes into sending mail.  You can configure postfix or sendmail to use your ISP email account to send mail which is the easiest way.  What flavor of linux are you using?