Here’s a quick video (3 minutes) that shows the use of Quickmail in Moodle. Quickmail is a popular 3rd party addon that provides email like functionality within Moodle (an alternative to the somewhat confusing default core messaging system). The video was created by Bergen Community College and is hosted on their channel.
Direct video link: http://www.youtube.com/watch?v=MJBWf_lCFLU