Mail are not been sent when sender email id has German character or any specials character in it, using codeigniter

Question

my codeigniter code is working fine for sending mail when the user fill a form and send it, the only issue is when the user has an email id with a special character in it like **Kurfürst@gmail.com or Müller@mail.com mail is not been sent below is my code it give form validation error

// ==================================================================================================

                    $emails = $this->Req_model->fetch_all_emails();

                    foreach($emails as $email){
                        mb_internal_encoding("UTF-8"); 
                        $subject = mb_encode_mimeheader($subject,'UTF-8','Q');
//$msg2 = "From: ".$userEmail."\n\n";
// $headers = "MIME-Version: 1.0" . "\r\n";
//$headers = "Content-type:text/plain;charset=UTF-8" . "\r\n";
$headers = "From: ".$userEmail . "\r\n";
// mb_internal_encoding("UTF-8"); 
//                         $headers = mb_encode_mimeheader($headers,'UTF-8','Q');

$msg2 = "Dienstleistung: ".$dep."\n";
$msg2 .= "Name: ".$surname."\n";
$msg2 .= "Telefon: ".$contact."\n";
$msg2 .= "E-Mail: ".$userEmail."\n";
$msg2 .= "Häufigkeit: ".$second_dropdown."\n";
$msg2 .= "Nachricht: ".$address."\n";

                        $msg2 = wordwrap($msg2,70);
                        mail($email['email'],"[sometext] Anfrage Dienstleistung ".$surname, $msg2, $headers);
                    }

below is my validation code

<script style="user-select: auto;">



    $(document).on("click","#sumbitbtnform", function(e){
      e.preventDefault()
      var data = {}

  if(!($("#department").val().length > 0) || !($("#userEmail").val().length > 0)  || !($("#userName").val().length > 0) || !($("#second_dropdown").val().length > 0) || !($("#address").val().length > 0) || !($("#userContact").val().length > 0)){
    $("#form-reject").css('display', "block")
    const timeout = document.getElementById("form-reject")
    setTimeout(hideElement, 2000) //milliseconds until timeout//
  function hideElement() {
    timeout.style.display = 'none'
  }
  }else{
    let today = new Date();

    let date = today.getDate()+'-'+(today.getMonth()+1)+'-'+today.getFullYear();
    console.log("fjnskj")
      data.department = $("#department").val()
      data.email = $("#userEmail").val()
      data.date = date
      data.surname = $("#userName").val()
      data.contact = $("#userContact").val()
      data.address = $("#address").val()
      data.service_interval = $("#second_dropdown").val()
      var url = "https://mywebiste.com//requirements/req_form"



      $.ajax({
      url:url,
      data: data,
      method:"post",
      success:function(dat){
        console.log(dat)
        $('#jobAddedSuccsessfuly').modal('show');
        
      }
      })
      }


      })

  </script> ```

how can I solve it