Validate an E-Mail Address with PHP, the Right Way

Jun 01, 2007 By Douglas Lovell

Listing 9. A Complete E-mail Validation Function

/**
Validate an email address.
Provide email address (raw input)
Returns true if the email address has the email
address format and the domain exists.
*/
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;
}

Spread the word! There is some danger that common usage and widespread sloppy coding will establish a de facto standard for e-mail addresses that is more restrictive than the recorded formal standard. If you want to fool the spambots, adopt an e-mail address like, {^c\@**Dog^}@cartoon.com. Unfortunately, you might fool some legitimate e-commerce sites as well. Which do you suppose will adapt more quickly?

Douglas Lovell is a software engineer with IBM Research, author of The XSL Formatting Objects Developer's Handbook published by Sams, and Web site editor for iac52.org.