56. The machine-readable storage medium of claim 55 , wherein the step of sending the request for the reputation score of the message sender comprises sending a DNS request and receiving the response to the request for the reputation score of the message sender comprises receiving a DNS response.
55. The machine-readable storage medium of claim 39 , further comprising instructions which, when executed by the one or more processors, cause the one or more processors to carry out the step of sending a request for the reputation score of the message sender to a service for determining the reputation of the message sender, and wherein the step of obtaining the reputation score of the message sender comprises receiving a response to the request for the reputation score of the message sender from the service for determining a reputation of the message sender.