This is a simple little PHP script I wrote to hide e-mail addresses from computers that scan the Internet for e-mail addresses to spam. The script converts any e-mail address into an e-mail address link that is displayed in any javascript enabled browser using a javascript document.write() function.

<?
/**
 * hideEmail Version 1.0 // 2005-06-22
 * by Brent O'Connor (http://brent.epicserve.com)
 *
 * This function converts any email address into javascript
 * document.write function that prints the email address as an html
 * link.
 * @param string $email - The email address you want to hide from
 *   email spiders.
 * @param string $display - The string you want to display for link
 *   if you don't want to use the email address itself.
 * @param string $subject - The subject of your email if you want
 *   one.
 * return string
 * 
 * Examples:
 * hideEmail('username@domain.com');
 * hideEmail('username@domain.com', 'Contact Me');
 * hideEmail('username@domain.com', 'Contact Me',
 *   'Some Stupid Subject');
 */
function hideEmail($email, $display = NULL, $subject = NULL) {

    $pattern = '/^([\.a-zA-Z0-9_-]+)@([\.a-zA-Z0-9_-]+)\.'.
      '([\.a-zA-Z0-9_-]+)$/';
    preg_match($pattern, $email, $emailArr);
    $username = $emailArr[1];
    $domain   = $emailArr[2];
    $ext      = $emailArr[3];

    if (empty($display)) {
        $display = "' + '".$username."' + '@' + '".
            $domain."' + '.' + '".
        $ext."' + '";
    }
    if (!empty($subject)) {
        $subject = "?subject=$subject";
    }

    $return_value = "";

    return $return_value;

}
?>

This is an example of how you can use this script to protect e-mail addresses that you are displaying from some kind of contact information database.

Example:

<?
while($row = mysql_fetch_array($result) {
<?= hideEmail($row['email'] ?>
}
?>

I plan on writing another function that works in conjunction with hideEmail that will find existing e-mail links in a large body of text and then convert them to a spam safe e-mail address.

Update:

The following is the code I came up with for using hideEmail with large text blocks that might contain multiple mailto links.

<?
/**
 * This function finds all the mailto links in a large body of
 * text and then sends them to the function hideEmail() which
 * then replaces the mailto link with a javascript link that is
 * hidden from computers scanning the net for e-mails to spam.
 * @param string $text The large body of text that contains
 *   mailto links.
 * @return string
 *
 * Example useage:
 * <? echo hideEmailsInTextBlock($text) ?>
 * <? $text = hideEmailsInTextBlock($text) ?>
 */
function hideEmailsInTextBlock($text) {

  $pattern = '/]*)\shref="mailto:([^>]*)">([^<]*)<\/a>/';
  $text = preg_replace_callback(
    $pattern,
    create_function(
      '$matches',
      'return hideEmail($matches[2], $matches[3], "Testing, 123");'
    ),
    $text
  );

  return $text;

}
?>