Son-in-law...
The mother-in-law comes home and finds her son-in-law furious and packing his suitcase. "What happened?" "What happened? - I'll tell you what happened! I sent an email to my wife saying that I was coming home from my trip today. I got home and guess what I found?... My wife, yes my Rachel, with another guy in our marital bed! This is the end of our marriage, I will leave forever!" "Calm down!" says mother-in-law. "There is something odd about this story. Rachel would never do such a thing! Wait a minute while I check what happened." Moments later, mother-in-law comes back with a big smile. "You see, I said there must be a simple explanation... Rachel didn't get your email."