I'm SO excited that I can finally enable e-mail on my self-hosted drupal sites! This is going to make the whole thing much more fun.
The long and short of this story is that when you set up a drupal powered website on your computer at home you can try to use the built in e-mail systems, but nothing will happen. The reason is that your home server most likely doesn't have email subsystems installed, and even if it did your ISP no doubt blocks outgoing e-mail ports to prevent spam from being sent by home users.