6. A method as in claim 5 , wherein an attribute of the set of attributes is a number of user identifiers in the header of an email from which a fact of the set of facts was formed; wherein assigning the fact score to the fact based on the attribute includes: generating a fact score based on the number of user identifiers in the header of the email, the fact score decreasing with an increasing number of user identifiers in the header of the email and increasing with a decreasing number of user identifiers in the header of the email.
5. A method as in claim 3 , wherein the PIM server includes an email server that accesses an email database, the email database including a set of emails, each email of the set of emails including a header and a body, the header including references to user identifiers, the body including a message; and wherein obtaining the set of facts from the PIM server includes: parsing the header and the body of an email of the set of emails to form, as a fact of the set of facts, a relationship between user identifiers, references to which are included in the header.