Checks if an email is a valid RFC 2822 email address

validate_rfc_2822_email.function.php

<?php

/**
 * Checks if an email is a valid RFC 2822 email address
 *
 * Examples:
 * <code>
 * <?php
 * validate_email('[email protected]');                // returns true
 * validate_email('Felds Liscia <[email protected]>'); // returns false
 * ?>
 * </code>
 *
 * @author  Felds Liscia <[email protected]>
 * @version 2011-03-10
 * @see     http://www.regular-expressions.info/email.html
 * @param   string $email The email to be validated
 * @return  bool
 */
function validate_rfc_2822_email($email)
{
  $regexp = '/^(?:[a-z0-9!#$%\'*+\/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&\'*+\/=?^_`{|}'.
            '~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\['.
            '\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-'.
            '9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-'.
            '9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?'.
            '|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-' .
            '\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])$/';

  return (bool) preg_match($regexp, $email);
}