Spammers are not abe to prevent intermediary systems from adding these headers while the headers provide only minimal protection because a thorough examination of the "Received:" header will be required to identify the real source of the message.
There are two popular techniques used by spammers to puzzle message recipients: using open relay sites (Yahoo! Anti-Spam Resource Center, 2004) to send messages and adding "Received:" headers of their own creation when sending a message. Open relay sites refer to servers that are generally allowed to be used by unknown computers in order to to send e-mail messages. Mail can be traced back to these relays, but it is unlikely that the relay operator will be able to identify the system that passed it the message. While servers that allow relaying are becoming less common as a result of the spam problem, they still exist and are well-known by spammers. These relay sites are often blacklisted, meaning that certain ISPs will not accept messages from them. While this is helpful, it has the effect of blocking not only spam, but also legitimate messages by other senders that may depend on the relay for mail transport.
The second technique is the adding of bogus "Received:" headers. However, this technique is not so effective as the first one. The bogus headers usually contain errors, but are not able to prevent the addition of accurate "Received:" headers. This means that recipient can believe the header that the own server added (jupiter.solar.net in the example) and work back from one header to the next, identifying whether the server is one he trusts at each step. (Klensin, 1995) The message "id" can be utilized to authenticate the validity with the administrator at each intermediary. Ultimately, the false headers can...
The problem of spam has grown intensively since the emergence of the Internet. During the period of 2001-2002, spam increased by 450 percent or 12.4 billion messages per day. Spam is considered to be highly challenging problem because it mostly contains pornographic advertisement or fraudulent, get-rich-quick schemes sent from a cautiously disguised source. Spam is also a computer security risk since it spreads computer viruses that then turn infected computers into spammers. The sending of spam results in a substantial shifting of costs from advertisers to ISPs and e-mail recipients. In 2003, spam is counted to have cost companies worldwide $20.5 billion. Spammers are able to send messages for minimal cost--the cost of their Internet access and mailing lists. The costs of relaying messages, storing them, and downloading them are borne by others. The extent of other forms of commercial advertising that occurs is limited by the cost of the advertising.