This seem to be pretty new, never seen it in the wild yet.

PR with a patch and unit test welcome.

hi @ll

here my solution, for multiple-emails

$.validator.methods.email = function(value, element, no_multiple) {
  if (this.optional(element)) {
    return true;
  }
  if (!element.multiple || !no_multiple) {
    return /^[a-zA-Z0-9.!#$%&'*+\/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$/.test(
      value
    );
  } else {
    var emails = value.split(/[,]+/); // split element by ,
    valid = true;
    for (var i in emails) {
      value = emails[i];
      valid =
        valid &&
        $.validator.methods.email.call(this, $.trim(value), element, false);
    }
    return valid;
  }
};

i hope it helps

See also: https://stackoverflow.com/questions/10352221/jquery-validation-plugin-multiple-email-addresses#10352428, so it has existed in the wild for over 5 years now.

My function is for the HTML5 element input-type = "email" with and without the attribute multiple
<input id="email1" name="email1" type="email" multiple>

It verifies by itself whether it is multiple and then makes the right test

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