$re = '/[A-Za-z0-9_-]+@mycompany\.com/';
$str = 'user@mycompany.com
user@anothercompany.com
user-123@mycompany.com
first-last@mycompany.com
first_last@mycompany.com
user22!@mycompany.com
';
preg_match_all($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