How to throw an errors if the emails already exists?

Hey, I have 3 email fields in my form L1 EMAIL L2 EMAIL L3 EMAIL the emails entered I this should not be the same to any of the email entered before it should be unique to that of the previous form. If any of the emails is the same as that of the previous forms it should throw an error. I tried using doing duplicate value but it validates only one field data and not all the three email text boxes.

Can you please help me with a proper solution as duplicate value validator doesn't support one than field value/data