E-Mail Validation Program

I found this important program for validating the email-ids it:

• checks for the correct format of e-mail id
• checks for valid domain part of e-mail id
• returns true or false.

function validEmail($email)

{

$isValid = true;

$atIndex = strrpos($email, "@");

if (is_bool($atIndex) && !$atIndex)

{

$isValid = false;

}

else

{

$domain = substr($email, $atIndex+1);

$local = substr($email, 0, $atIndex);

$localLen = strlen($local);

$domainLen = strlen($domain);

if ($localLen < 1 || $localLen > 64)

{

// local part length exceeded

$isValid = false;

}

else if ($domainLen < 1 || $domainLen > 255)

{

// domain part length exceeded

$isValid = false;

}

else if ($local[0] == '.' || $local[$localLen-1] == '.')

{

// local part starts or ends with '.'

$isValid = false;

}

else if (preg_match('/\\.\\./', $local))

{

// local part has two consecutive dots

$isValid = false;

}

else 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

(!preg_match('/^(\\\\.|[A-Za-z0-9!#%&`_=\\/$\'*+?^{}|~.-])+$/',

str_replace("\\\\","",$local)))

{

// character not valid in local part unless

// local part is quoted

if (!preg_match('/^"(\\\\"|[^"])+"$/',

str_replace("\\\\","",$local)))

{

$isValid = false;

}

}

if ($isValid && !(checkdnsrr($domain,"MX") || checkdnsrr($domain,"A")))

{

// domain not found in DNS

$isValid = false;

}

}

return $isValid;

}