Listing 1: Shows an example code that contains 3 errors. First, it fails to recognize many valid e-mail address characters, such as %. Secondly, it splits the e-mail address into username and domain parts at the sign @. E-mail addresses that contain a quoted @ sign, such as koko\@koko@domain.com will break this code. Lastly, it fails to check for host address DNS records. function validateEmail($email_add) { if (preg_match(”/^([a-zA-Z0-9])+([a-zA-Z0-9\._-])*@([a-zA-Z0-9_-])+( [a-zA-Z0-9\._-]+)+$/”, $email_add)) { list ($username, $domain)=split(‘@’,$email_add); if (!checkdnsrr($domain, ‘MX’)) { return false; } return true; } return false; } Listing 2: Shows a better way to develop an E-mail validator as it satisfy the following requirements: -An e-mail address consists of local part and domain seperated by an at sign (@) character (RFC 2822 3.4.1)/ -The local part may consist of alphabet and numeric characters, and the following characters: !#$%&’*+-/=?^_`{|}~, possibly with dot seperators (.), inside, but not at the start, end or next to another dot seperator (RFC 2822 3.2.4) -The local part may consist of a quoted string - i.e. anything within quotes (”), including spaces (RFC 2822 3.2.5) -Quoted pairs (such as \@) are valid components of a local part, though an obsolete form from RFC 822 (RFC 2822 4.4) -The maximum length of a local part is 64 characters (RFC 2821 4.5.3.1) -A domain consists of labels seperated by dot seperators (RFC 1035 2.3.1) -Domain labels start with an alphabet character followed by 0 or more alphabet characters, numeric characters or hyphen (-), ending with an alphabetic or numeric character (RFC 1035 2.3.1) -The maximum length of a label is 63 characters (RFC 1035 2.3.1) -The maximum lenght of a domain is 255 characters (RFC 2821 4.5.3.1) -The domain must be fully qualified and resolvable to a type A or type MX DNS address record (RFC 2821 3.6) function validateEmail($email_add) { $isValid = true; $atIndex = strrpos($email_add, “@”); if (is_bool($atIndex) && !$atIndex) { $isValid = false; } else { $domain = substr($email_add, $atIndex+1); $local = substr($email_add, 0, $atIndex); $localLen = strlen($local); $domainLen = strlen($domain); if ($localLen < 1 || $localLen > 64) { $isValid = false; // local part lenght exceeded } else if ($domainLen < 1 || $domainLen > 255) { $isValid = false; // domain part lenght exceeded } else if ($local[0] == ‘.’ || $local[$localLen-1] == ‘.’) { $isValid = false; // local part starts or ends with ‘.’ } else if (preg_match(’/\\.\\./’, $local)) { $isValid = false; // local part has 2 consecutive dots } else if (!preg_match(’/^[A-Za-z0-9\\-\\.]+$/’, $domain)) { $isValid = false; // character not valid in domain part } else if (preg_match(’/\\.\\./’, $domain)) { $isValid = false; // domain part has 2 consecutive dots } else if (!preg_match(’/^(\\\\.|[A-Za-z0-9!#%&`_=\\/$\’*+?^{}|~.-])+$/’ . str_replace(”\\\\”.”",$local))) { if (!preg_match(’/^”(\\\\”|[^”])+”$/’, $str_replace(”\\\\”,”", $local))) { $isValid = false; //character not valid in local part unless local part is quoted } } if ($isValid && !(checkdnsrr($domain, “MX”) || checkdnsrr($domain, “A”))) { $isValid = false; // domain not found in DNS } } return $isValid; }
Source: http://www.ArticlePros.com/author.php?Max Teo
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