A method comprising: receiving a confirmation request at a sending email system from a receiving email system to confirm that an electronic message sent to an intended recipient was sent on behalf of an originator identified in the electronic message, the electronic message including a first data string purportedly generated by application of a first algorithm to a portion of said electronic message and further including said portion of said electronic message; generating a second data string by said sending email system, by application of a second algorithm to said portion of said electronic message included in said confirmation request; comparing said first data string to said second data string by said sending email system; if said comparing determines that said first data string does not match said second data string, responding to said confirmation request by said sending email system to said receiving email system, denying said electronic message was sent on behalf of the originator identified in the electronic message due to the originator using a false originating address; and if said comparing determines that said first data string matches said second data string, responding to said confirmation request by said sending email system to said receiving email system, affirming said originator identified in the electronic message did not send said electronic message from a false originating address; wherein the second algorithm applied to the portion of the electronic message to generate said second data string is selected by said sending email system from a plurality of algorithms based on a time associated with the electronic message. receiving a confirmation request at a sending email system from a receiving email system to confirm that an electronic message sent to an intended recipient was sent on behalf of an originator identified in the electronic message, the electronic message including a first data string purportedly generated by application of a first algorithm to a portion of said electronic message and further including said portion of said electronic message; generating a second data string by said sending email system, by application of a second algorithm to said portion of said electronic message included in said confirmation request; comparing said first data string to said second data string by said sending email system; if said comparing determines that said first data string does not match said second data string, responding to said confirmation request by said sending email system to said receiving email system, denying said electronic message was sent on behalf of the originator identified in the electronic message due to the originator using a false originating address; and if said comparing determines that said first data string matches said second data string, responding to said confirmation request by said sending email system to said receiving email system, affirming said originator identified in the electronic message did not send said electronic message from a false originating address; wherein the second algorithm applied to the portion of the electronic message to generate said second data string is selected by said sending email system from a plurality of algorithms based on a time associated with the electronic message.