$re = '/(?i:([;]|^)([a-z0-9.]+@(dom\.net|part1\.part2\.uk))(?=[;]|$))/';
$str = 'a.name@part1.part2.uk;a.name@dom.net';
preg_match_all($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