Or WTF is SPF, DKIM and DMARC?
So a girl is in a bar (this is the 80s afterall). Random people keep buying her drinks. But she only wants drinks from her Boyfriend (who, inexplicably, is on the other side of the bar). She knows the boyfriend will buy her nice drinks that aren’t spiked or are nasty. Like Carling.
Problem is, a lot of random people tell the barman that they’re our heroine’s boyfriend. So the girl points out the person who is the real Boyfriend to the barman. Now the barman will only accept drinks from the guy pointed out by the girl. This is SPF.
But the random people get crafty and start dressing like the Boyfriend, and doing their hair like him, etc. So the Boyfriend starts signing each drink to prove it’s from him. This is DKIM.
The barman and girl think this is all a great idea, and they start collecting the names of all the random people trying to send her unsolicited drinks. Then the girl can use this information to report the persistent creeps. This is DMARC.
The girl gives the list to the bouncers. They’re already aware of some of the people and have put them on the ‘banned’ list which is distributed to other bars. This is an RBL.