Hex to ASCII:

   function hex2asc ($strMail) {
     for ($i=0; $i<strlen($strMail)/2; $i++) {
        $asc = '';
        $asc.=chr(base_convert(substr($strMail,$i*2,2),16,10));
     }
     return $asc;
   }

to unicode:

   function uni_encode ($strMail) {
      $encoded = bin2hex("$strMail");
      $encoded = chunk_split($encoded, 2, '%');
      $encoded = '%' . substr($encoded, 0, strlen($encoded) - 1);
      return $encoded;    
   }

to hex :

   function hex_encode($strMail)
   {
     $ret_string = '';
     $len = strlen($strMail);
     for ($x=0; $x<$len; $x++){
         $ord=ord(substr($strMail, $x, 1));
         $ret_string .= "&#$ord;";
     }
     return $ret_string;
   }