Abstract: An originating email server is authenticated by a destination email server using a public key provided by the originating email server, thereby making it possible to detect an email with a forged origination address with no action required by a domain owner. A personal computer is authenticated using a reputation report associated with a unique number corresponding to the personal computer, enabling, in one embodiment, spam detection, and, in another embodiment, a decision that a valid user is requesting service registration at a website.

Abstract: An originating email server is authenticated by a destination email server using a public key provided by the originating email server, thereby making it possible to detect an email with a forged origination address with no action required by a domain owner. A personal computer is authenticated using a reputation report associated with a unique number corresponding to the personal computer, enabling, in one embodiment, spam detection, and, in another embodiment, a decision that a valid user is requesting service registration at a website.

Abstract: The portion of email traffic that cannot be definitively determined to be spam or definitively determined to be ham (non-spam) is processed by sending a bounceback email to the sender, requiring the sender to reply using a sub-address created by the bounceback generator. The type of bounceback email depends on whether the domain of the received email indicates that the sender is or is not likely to be a spammer. When the sender is not likely to be a spammer, the bounceback email includes a sub-address in computer readable form. When the sender is likely to be a spammer, the bounceback email includes a test that must be solved to yield the sub-address; preferably, the test is very difficult for a computer to solve but reasonably easy for a human to solve. When a reply email to the bounceback email (“reply bounceback”) is received, the presence of the sub-address indicates that the sender is not a spammer, so the reply bounceback is determined to be ham and delivered to the destination mailbox.

Abstract: The portion of email traffic that cannot be definitively determined to be spam or definitively determined to be ham (non-spam) is processed by sending a bounceback email to the sender, requiring the sender to reply using a sub-address created by the bounceback generator. The type of bounceback email depends on whether the domain of the received email indicates that the sender is or is not likely to be a spammer. When the sender is not likely to be a spammer, the bounceback email includes a sub-address in computer readable form. When the sender is likely to be a spammer, the bounceback email includes a test that must be solved to yield the sub-address; preferably, the test is very difficult for a computer to solve but reasonably easy for a human to solve. When a reply email to the bounceback email (“reply bounceback”) is received, the presence of the sub-address indicates that the sender is not a spammer, so the reply bounceback is determined to be ham and delivered to the destination mailbox.

Abstract: An originating email server is authenticated by a destination email server using a public key provided by the originating email server, thereby making it possible to detect an email with a forged origination address with no action required by a domain owner. A personal computer is authenticated using a reputation report associated with a unique number corresponding to the personal computer, enabling, in one embodiment, spam detection, and, in another embodiment, a decision that a valid user is requesting service registration at a website.