This post is over 3 years old, so please keep in mind that some of its content might not be relevant anymore.
After having setup an email server (eg: using gmail as smtp server or sendmail as a SMART HOST or any other way you want..) you need to test it.
The quickest way, for me, is to do:
mail -s Test [email protected] < /dev/null
This will send an email with no body text.
Enjoy!