Of course, you can always just delete the unwanted message. It is against the MITnet Rules of Use to send bulk e-mail. This is true whether you include the recipient usernames individually or use a mailing list. When a user sends out an announcement to a huge list of recipients, the mail servers get overloaded, disks fill up, and staff intervention is required. The result is a degradation of service for all users.
Chain mail is especially abusive of the system.
Thou shalt not annoy. Thou shalt not be easily annoyed. If you receive e-mail that is of a more disturbing or harassing nature than a spam, there are steps you can take. First, let the sender know that you do not wish to receive any more mail from him or her. If you continue to receive mail, MIT offers several avenues to address the problem.