abg: there are technologies which can stop such forgeries, but they do no good until people start using them. This means that the people who run domains have to publish the right data, and the people running MTAs have to install tools which check it.

Right now, there is absolutely no reason for anyone to ever accept a single mail which forges one of my domains. It still happens, because nobody has gone to the trouble of adding the necessary magic to their mail servers. They're mad about getting spam, I'm mad about getting forged, and yet there they sit.

It'll probably take some kind of huge concerted forging effort to make most people go to the trouble of running checks. Everything else seems to happen that way.