An e-mail filtering method and system that categorize received e-mail messages based on information about the sender. Data about the sender is contained in the message and is used to identify the actual sender of the message using a signature combining pieces of information from the message header or derived from information in the message header. This and other information about the message is then sent by each member of an e-mail network to one or more central databases (in one embodiment, the information will also be stored at a database associated with the recipient's e-mail program and filtering software) which stores the information and compiles statistics about e-mails sent by the sender to indicate the likelihood that the e-mail is unsolicited and determine the reputation of the sender (a good reputation indicates the sender does not send unwanted messages while a bad reputation indicates the sender sends unsolicited e-mail messages). Information from the central database is then sent to recipients in order to determine the likelihood that a received e-mail message is spam (information may also be obtained from the local database associated with the recipient's e-mail program and filtering software).