As Kelly Thompson says, they're dealing with a group of people with the personality that prevents them from just hitting delete. Andrew Conry-Murray, business editor, really wanted to work in a reference to Monty Python's famous Spam sketch, but just couldn't find a way. An open relay is an e-mail server that forwards mail between sending and receiving machines, both of which are outside the administrative domain of the forwarding server. By contrast, a closed relay will only pass along mail if the sender or receiver is under the same administrative control as the relay. Nowadays, open relays are akin to accepting luggage from a stranger at the airport and agreeing to deliver it-you don't know any of the people involved or the suitcase's contents.
Spammers gain a pair of benefits from mail relay.
While it's possible to trace the original sender, the relay helps to cover a spammer's tracks. The second is that the spammer hijacks the resources of the open relay, which may have a powerful processor and high-speed Internet connection. In many cases, network administrators are not even aware that their servers are vulnerable to third-party relay. Kelly Thompson, a product manager for the MAPS RBL list, says there are several ways this can happen. In some instances, administrators may set up servers that they don't intend to use for mail, but the server software contains a mail program.