Abstract: A recipient computer system may receive one or more electronic messages. The recipient computer system may send one, two, or more challenge messages to the sender of the electronic messages in determining whether to deliver the electronic message. The recipient computer system may accept or reject an electronic message based on the response, or lack of response, to the challenge messages. The recipient computer system may send two or more challenge messages at intervals. A sender computer system may record activity of the sender computer system for a recipient computer system to use in determining whether to deliver an electronic message. A sender computer system may provide a summary of that activity with an electronic message. A sender computer system may provide an authorization key for a recipient computer system to use in determining whether to deliver an electronic message. The authorization key may be generated by a third party.

Abstract: A system may include an electronic messaging system that may access user identifier information, which may be used to identify self-addressed electronic messages. The electronic messaging system may determine how to process an incoming electronic message using at least a portion of the user identifier information. The electronic messaging system determines whether to send a challenge-response message to a sender of an electronic message using at least a portion of the user identifier information. The electronic messaging system may be configured to identify self-addressed electronic messages and, in response to such identification, process the messages appropriately.

Abstract: A recipient computer system may receive one or more electronic messages. The recipient computer system may send one, two, or more challenge messages to the sender of the electronic messages in determining whether to deliver the electronic message. The recipient computer system may accept or reject an electronic message based on the response, or lack of response, to the challenge messages. The recipient computer system may send two or more challenge messages at intervals. A sender computer system may record activity of the sender computer system for a recipient computer system to use in determining whether to deliver an electronic message. A sender computer system may provide a summary of that activity with an electronic message. A sender computer system may provide an authorization key for a recipient computer system to use in determining whether to deliver an electronic message. The authorization key may be generated by a third party.