Please try to be considerate of other people when you are using the computer system to communicate. While there are sometimes legitimate reasons to send electronic mail to people you don't know, those reasons certainly do not extend to sending them chain letters, unsolicited mass mailings (mail to a large number of recipients), or similar communications. In addition to annoying a large number of people, mass mailings are of particular concern because they take up considerable disk space and can affect the processing of other mail.
Also, note that section 5 of the Boston University Conditions of Use and Policy on Computing Ethics prohibits transmission of offensive, annoying, or harassing material. Anyone who uses a computer system at Boston University to send chain letters or otherwise annoy or harass people risks (minimally) losing his or her account.