Create table Person 
 (
 Id int primary key identity(1,1) not null,
 Email varchar(255) not null,
 )

 insert into Person(Email) values ('john@example.com'),('bob@example.com'),('john@example.com ')

delete 
    p1 
from 
    Person p1,
    Person p2 
where 
    (p1.email = p2.email) and (p1.id > p2.id)
  select Email from Person