public function addHeader($headerFieldNameOrLine, $fieldValue = null)
	{
		$this->getHeaders()->addTextHeader($headerFieldNameOrLine, $fieldValue);
		return $this;
	}
public function addHeader($headerFieldNameOrLine, $fieldValue = null)
	{
		$this->getHeaders()->addTextHeader($headerFieldNameOrLine, $fieldValue);
		return $this;
	}
public function addHeader ( $ headerFieldNameOrLine , $ fieldValue = null ) { $ this -> getHeaders ( ) -> addTextHeader ( $ headerFieldNameOrLine , $ fieldValue ) ; return $ this ; }
Check if message needs to be sent as multipart
MIME message or if it has only one part.

@return  bool
Check if message needs to be sent as multipart MIME message or if it has only one part .