$re = '/^\w+((-\w+)|(\.\w+))*\@[A-Za-z0-9]+((\.|-)[A-Za-z0-9]+)*\.[A-Za-z0-9]+$/m';
$str = 'me@too.dk
me.too@meee.dk
me,too@meee.dk
me.too@meee,dk
me-too@meee.dk
me.too.tt@meee.dk
me.too@meee.uk.dk
me.too@meee.co.dk';
preg_match_all($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