27. The invention of claim 25 , wherein the logic when executed is further operable to perform: extracting a domain name portion of the third network resource identifier; retrieving one or more MX records for the domain name portion from a domain name system (DNS) server; retrieving network address records for each mail exchange that is identified in the one or more MX records; determining an average reputation score for the network address records; adding the third network resource identifier to the blocklist when the average reputation score is less than a specified threshold.
27. The invention of claim 25 , wherein the logic when executed is further operable to perform: extracting a domain name portion of the third network resource identifier; retrieving one or more MX records for the domain name portion from a domain name system (DNS) server; retrieving network address records for each mail exchange that is identified in the one or more MX records; determining an average reputation score for the network address records; adding the third network resource identifier to the blocklist when the average reputation score is less than a specified threshold. 28. The invention of claim 27 , wherein the logic when executed is further operable to perform determining a blocklist status for the network address records, and adding the third network resource identifier to the blocklist when the blocklist status indicates that network addresses in the network address records are blocked.