Check the code below, it should do the job fine.
<?php
function get_domain($url)
{
$pieces = parse_url($url);
$domain = isset($pieces['host']) ? $pieces['host'] : $pieces['path'];
if (preg_match('/(?P<domain>[a-z0-9][a-z0-9\-]{1,63}\.[a-z\.]{2,6})$/i', $domain, $regs)) {
return $regs['domain'];
}
return false;
}
print get_domain("http://mail.somedomain.co.uk"); // outputs 'somedomain.co.uk'
?>