Listing 7. Domain Checks

if (!preg_match('/^[A-Za-z0-9\\-\\.]+$/', $domain))
{
   // character not valid in domain part
   $isValid = false;
}
else if (preg_match('/\\.\\./', $domain))
{
   // domain part has two consecutive dots
   $isValid = false;
}
else if (!(checkdnsrr($domain,"MX") || checkdnsrr($domain, "A")))
{
   // domain not found in DNS
   $isValid = false;
}