https://ahmetimamoglu.com.tr/php-utf-8-mail-gonderme-ornegi

Php-Utf-8-Email-Example1.php

<?php

function mail_utf8($from,$from_name,$to,$adi,$subject,$body=''){

   // Konu
   $subject = "=?UTF-8?B?".base64_encode(urldecode($subject))."?=";

   // Header bilgisi
   $headers  = 'MIME-Version: 1.0' . "\r\n";
   $headers .= 'Content-type: text/html; charset=utf-8' . "\r\n";
   $headers .= "Content-Transfer-Encoding: 8bit\n";
   $headers .= 'From: =?UTF-8?B?'.base64_encode(urldecode($from)).'?=<'.urldecode($from_name).'>' . "\r\n";

   // Gönder
   if(mail($to, $subject, $body, $headers)){
       return TRUE;
   }else{
       return FALSE;
   }    
}

Php-Utf-8-Email-Example2.php

<?php
// Mail İçeriği
$body ='
<table>
    <tr>
        <td style="border:1px solid #ddd;padding:5px">Adı Soyadı</td>
        <td style="border:1px solid #ddd;padding:5px">'.urldecode($_POST["adi"]).'</td>
    </tr>

    <tr>
        <td style="border:1px solid #ddd;padding:5px">Başlık</td>
        <td style="border:1px solid #ddd;padding:5px">'.urldecode($_POST["baslik"]).'</td>
    </tr>

    <tr>
        <td style="border:1px solid #ddd;padding:5px">İçerik</td>
        <td style="border:1px solid #ddd;padding:5px">'.urldecode($_POST["icerik"]).'</td>
    </tr>
</table>';


if (mail_utf8('gonderen_adres@ornek.com','Gönderen Adres','gidecek_adres@ornek.com',$_POST['adi'],$_POST['baslik'],$body)){
    echo 'Mail Gönderildi';
}else{
    echo 'Mail Gönderilirken Bir Hata Oluştu.';
}