1. A method for screening Diameter messages within a Diameter signaling router (DSR) having a distributed message processor architecture, the method comprising: at a DSR comprising a plurality of Diameter message processors, each configured to perform at least one Diameter function: receiving, at an ingress Diameter message processor of the Diameter message processors, a Diameter message from a Diameter peer node; identifying, at a Diameter application message processor of the Diameter message processors, a Diameter message screening rule associated with the received Diameter message, wherein the identified Diameter message screening rule specifies a maximum receipt rate for Diameter messages received from the Diameter peer node, wherein the Diameter messages received from the Diameter peer node are associated with a plurality of users; performing, at the Diameter application message processor of the Diameter message processors, a screening function associated with the identified Diameter message screening rule on the received Diameter message based on message attribute value pair (AVP) values, wherein performing the screening function on the received Diameter message includes determining that the Diameter message is to be discarded or is to receive additional screening, wherein performing the screening function on the received Diameter message includes adjusting a current receipt rate of Diameter messages associated with the identified Diameter message screening rule to account for the received Diameter message; after performing the screening function and determining that the Diameter message is to receive additional screening, performing a second screening function based on the maximum receipt rate for Diameter messages associated with the Diameter message screening rule; and in response to the current receipt rate of Diameter messages associated with the identified Diameter message screening rule exceeding the maximum receipt rate, routing the received Diameter message by forwarding the received Diameter message to an egress Diameter message processor of the Diameter message processors and notifying a network operator.