Patent ID: 8073912

Claim:
A method for authenticating a received email used by an email system, comprising: classifying the received email as either a first type or a second type based on whether the sender domain of the received email is associated with a spammer, when the received email is classified as the first type, sending a first type of bounceback email with a new sub-address to a sender of the received email, the first type of bounceback email having the new sub-address in computer-readable form, the new sub-address being appended to the origination email address in the bounceback email, and when the received email is classified as the second type, sending a second type of bounceback email to a sender of the received email, the second type of bounceback email having a test in a body of the second type of bounceback email, the test for differentiating a human from a machine and having a solution that is the new sub-address, wherein a destination address of a reply-to-bounceback email includes the new sub-address.