htmlpurifier/library/HTMLPurifier/AttrDef/URI/Email/SimpleCheck.php

<?php

/**
 * Primitive email validation class based on the regexp found at 
 * http://www.regular-expressions.info/email.html
 */
class HTMLPurifier_AttrDef_URI_Email_SimpleCheck extends HTMLPurifier_AttrDef_URI_Email
{
    
    public function validate($string, $config, $context) {
        // no support for named mailboxes i.e. "Bob <bob@example.com>"
        // that needs more percent encoding to be done
        if ($string == '') return false;
        $string = trim($string);
        $result = preg_match('/^[A-Z0-9._%-]+@[A-Z0-9.-]+\.[A-Z]{2,4}$/i', $string);
        return $result ? $string : false;
    }
    
}