What are the Attributes for the Reserved DeDupe Rules
Pete's answer should be correct, but reserved dedupe rules don't work like normal rules.  The original assumption: First name, last name and email must all be identical - is correct.

Dedupe rules with multiple criteria work by running a separate query for each criterion, filling a temp table with the weights.  This is flexible but inefficient, so the "reserved" queries are done using a single handwritten SQL query.  This particular query is found in CRM_Dedupe_BAO_QueryBuilder_IndividualSupervised::internal and overrides the stored query in the database (which is the old query from before reserved queries existed).  Here's the query that runs.

        SELECT contact1.id as id1, contact2.id as id2, {$rg-&gt;threshold} as weight
        FROM civicrm_contact as contact1
          JOIN civicrm_email as email1 ON email1.contact_id=contact1.id
          JOIN civicrm_contact as contact2 ON
            contact1.first_name = contact2.first_name AND
            contact1.last_name = contact2.last_name
          JOIN civicrm_email as email2 ON
            email2.contact_id=contact2.id AND
            email1.email=email2.email
        WHERE contact1.contact_type = 'Individual'");