Every single purely technical approach to stopping spam has been a complete loser.
In the fullness of time, the universe itself will die of heat. So what? What matters more is what use is made of time before it gets so "full." A number of purely technical approaches to stopping spam have been quite successful... in the short term... which not the same as being a complete loser in the long term. (Everything's a complete loser if you measure it right.)
There is no RFC or other public standards document which even attempts to define spam or explain, in a careful and professional manner, why it is a bad thing.
Someone else already quoted an RFC from geektools that contains such a definition. http://www.mail-abuse.org/standard.html, on the other hand, is something I cowrote back when I still had an operational role at MAPS, and still seems pretty careful and pretty professional (and pretty public.) -- Paul Vixie