$re = '/(?:\G(?!\A)|\[(?=[^][]*]))[^][",]*+(?:"[^"\\\\]*(?s:\\\\.[^"\\\\]*)*"[^][",]*)*+\K,/';
$str = '[["Sender", "mail@text.org"], ["Date", "Fri, 09 Jun 2017 13:29:22 +0000"]]';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php