private static function encodeBoundaryBlock($boundary, $contentType, $charset, $encoding, $content, $eol = "\n") {
		return '--' . $boundary . $eol
			. 'Content-Type: ' . $contentType. '; charset="' . $charset . '"' . $eol
			. 'Content-Transfer-Encoding: ' . $encoding . $eol . $eol 
			. self::encodeString($content, $encoding, $eol)
			. $eol . $eol;
	}