1. A method of facilitating the formation of groups of trustworthy members, the method comprising: inserting an invitation command into the header of a first e-mail message originating from an inviting group member; sending the first e-mail message to the e-mail client of an invitee; detecting the invitation command at the invitee's e-mail client; inserting an accept command into the header of a second e-mail message originating from the invitee; sending the second e-mail message to the e-mail client of the inviting group member; and detecting the accept command at the inviting group member's e-mail client, wherein the invitee becomes a new group member.