1. A method for routing electronic mail to a plurality of message transfer agents, each message transfer agent having a respective amount of resources that configures a message transfer agent to a performance level associated with a level of trust, the method comprising: receiving electronic mail traffic from a network source address; comparing the network source address to a stored list of network addresses; in response to determining that the network source address appears in the stored list of network addresses: determining a level of trust associated with the network source address; selecting a first message transfer agent of the plurality of message transfer agents based on the level of trust, each of the plurality of message transfer agents having a respective amount of resources that configures each message transfer agent to a performance level associated with a respective level of trust, and routing the electronic mail traffic to the first message transfer agent; and in response to determining that the network source address does not appear in the stored list of network addresses: assigning a particular level of trust to the network source address based on the electronic mail traffic and a threshold and a percentage of unknown recipients associated with previous traffic from the network source address; selecting a second message transfer agent of the plurality of message transfer agents based on the particular level of trust; and routing the electronic mail traffic to the second message transfer agent.