Sometimes, when I log into a box and 'su' to root, I get a cute little message saying I have mail (thank GOD it's not AOL).

- Where is this mail?
- What does it contain?
- Who/What sent it?
- How important is it?

Is this even actual "mail" in the same sense as email? Or is it just my system telling me something?

**EDIT:** In relation to [this][1] question, would I be able to send myself mail using the sendmail program like so: `email@localhost`?


  [1]: http://superuser.com/questions/306995/why-cant-i-email-myself-at-myemail74-125-235-55