A user's address book includes a first group of email addresses. Those email addresses are used to identify address books that include another group of email addresses. Multiple iterations may be used to identify several groups of email addresses, representing a user's social network. When an email message addressed to the user is received, the message is trusted if the sending email address is within the user's social network. Otherwise, the message is flagged as junk mail. Varying trust levels may be applied to messages that are received based on a distance within a social network between the sending email address and the user and/or how often the sending email address appears within the social network.