1. A method of classifying e-mails, the method comprising: receiving a plurality of e-mails that each include a respective header portion and content portion; storing the received plurality of e-mails; analyzing, using at least one processor, the content portions of the stored plurality of e-mails to cluster the plurality of e-mails into multiple groups of substantially duplicate e-mails; storing the multiple groups of substantially duplicate e-mails; selecting a test e-mail from a group of the stored multiple groups; determining a class for the test email based on the content portion of the test e-mail; and classifying a non-test e-mail in the group based on the determined class of the test e-mail.