code: protected function encodeHeader($str) {
  		if (extension_loaded('iconv')) {
  			$out = iconv_mime_encode('Subject', $str,
  				['input-charset' => 'UTF-8', 'output-charset' => $this->charset]);
  			$out = substr($out, strlen('Subject: '));
  		} elseif(extension_loaded('mbstring')) {
  			mb_internal_encoding('UTF-8');
  			$out = mb_encode_mimeheader($str, $this->charset, 'B', static::$EOL, strlen('Subject: '));
  		} else
  			$out = wordwrap($str,65,static::$EOL);
  		return $out;
  	}
docs: encode and split header strings
  @param $str
  @return string