Every time I need to build a registration form I face the problem of email validation: should it be done client side, and how?
This StackOverflow tread is the best resource on the argument I found whith a lot of examples, useful links and thoughts on why you shouldn’t validate email addresses client side.

Finally, even in discouraged, I used this function and I’m pretty satisfied.

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function validateEmail(email){
  
  var regExp = /^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)
               |(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]
               {1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;
  return regExp.test(email);
}