email address

my girlfriend is having an affair with a married man at work, she doesnt know I know! I found out through her email,I have the email address of the man but dont know who he is , could someone please tell me how I can find out through his email address!theres nothing I can do BUT I WOULD LIKE TO TELL THIS MANS WIFE BECAUSE HE HAS TWO CHILDREN AND IT MAKES ME SICK TO SEE THAT DONE TO A FAMILY!