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.