IBBoardToday in "big companies doing dumb shit": Yahoo Japan sent a rejection email to my server because an LY Corp server (the parent of Yahoo Japan) spoofed the MAIL FROM line and my domain sets a hard-fail in the SPF record.
THE WHOLE POINT OF A HARD FAIL IS TO SAY THAT IT'S NOT MY EMAIL AND YOU CAN THROW IT AWAY, YOU FREAKING IDIOTS!