Ok we all have some lil snippets of code we fall back on time-&-time again so I thought would be a nice idea to share some of them out

So I'll start it of......

this is a simple function I cobbled together after reading some tuts on validating email adresses with PHP

It checks email formatting and also that domain exsists - not foolproof but should help weed out things like adflhad@asdfhlsd.com

Code:
//check email is valid format
function emailsyntax_is_valid($email) {
  $to_work_out = explode("@", $email);
  if (!isset($to_work_out[0])) return FALSE;
  if (!isset($to_work_out[1])) return FALSE;

  $pattern_local = '^([0-9a-z]*([-|_]?[0-9a-z]+)*)(([-|_]?)\.([-|_]?)[0-9a-z]*([-|_]?[0-9a-z]+)+)*([-|_]?)$';
  $pattern_domain = '^([0-9a-z]+([-]?[0-9a-z]+)*)(([-]?)\.([-]?)[0-9a-z]*([-]?[0-9a-z]+)+)*\.[a-z]{2,4}$';
  $match_local = eregi($pattern_local, $to_work_out[0]);
  $match_domain = eregi($pattern_domain, $to_work_out[1]);

  if ($match_local && $match_domain) {
  	list($user, $domain) = split("@", $email, 2);
      if (! checkdnsrr($domain, "MX")) {
        return FALSE;
	}
	else
	{
    return TRUE;
	}
  }
  return FALSE;
}