$re = '/^([a-z][a-z0-9]{1,13}[_.\-]?[a-z0-9]{1,13})@((([0-9]{1,3})([.]{1})([0-9]{1,3})([.]{1})([0-9]{1,3})([.]{1})([0-9]{1,3}))|([a-z0-9]{1,10}[\-]?[a-z0-9]{1,10}[.]?[a-z0-9-]{1,10}[.]{1}[a-z]{2,4}))$/m';
$str = '//Valid
john.doe@mail.com
johndoe@mail.com
john-doe@mail.com
john_doe@mail.com
john123doe@mail.com
john123.doe@mail.com
johndoe456@mail.com
abc-d@mail.com
test@test.domain.com
test@127.1.1.1
test@test.domain.shop
// Invalid
abc-@mail.com
abc..def@mail.com
.abc@mail.com
abc#def@mail.com
123abc-d@mail.com
ABc@mail.com
test@sub.test.domain.com
test@test.domain.c';
preg_match_all($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