Me Irish in-laws

An Irish  mother-in-law arrives home from the shops to find her son-in-law Paddy in a steaming rage and hurriedly packing his suitcase. 
"What happened Paddy?" she asks anxiously. 
"What happened!  What happened?  I'll tell you what happened!  I sent an email to my wife telling her I was coming home today from my fishing trip.  I get home... and guess what I found?  Yes, your daughter, my wife Jean, naked with Joe Murphy in our marital bed!  This is unforgivable, the end of our marriage.  I'm done.  I'm leaving forever!" 
"Ah now, calm down Paddy...  Calm down," says his mother-in-law.  "There is something very odd going on here.  Jean would never do such a thing!  There must be a simple explanation.  I'll go speak to her immediately and find out what happened." 
Moments later, the mother-in-law comes back with a big smile. 
"Paddy.  I told you there must be a simple explanation... she never got your E-mail!"