1. A computer-implemented method of automatically organizing email messages, comprising: at a computer system: accessing a plurality of email message headers; identifying a set of email addresses included in the email message headers; excluding email addresses that occur fewer than a specified number of times in the plurality of email message headers from the identified set of email addresses; for a respective email address in the set of email addresses, determining whether the respective email address is a group email address or an individual email address; assigning respective weights to respective email addresses in the set of email message headers, wherein the assigning comprises weighting the respective email addresses based on respective inverse frequencies of occurrence of the respective email addresses in the plurality of email messages headers and applying a first weighting factor to group email addresses in the set of email addresses and a second weighting factor to individual email addresses in the set of email addresses, wherein the first weighting factor is different than the second weighting factor; dividing a plurality of email messages associated with the email message headers into a plurality of clusters in accordance with the respective weights; and providing email messages of the plurality of email messages for display, organized by the respective clusters.