DKIM Wizard: http://www.port25.com/support/domainkeysdkim-wizard/
 - Enter a domain and choose a selector to get your public and private keys
 - Create the two DNS records containing the public key
 - Note: The test seen on that site won't work with LMP implementation. To test DKIM, send to Yahoo or gmail and check message source/headers for a DKIM "pass" message.

Get php-dkim: http://downloads.sourceforge.net/project/php-dkim/php-dkim/v1.0/php-dkim.zip

Unzip php-dkim.zip

Modify dkim-cfg-dist.php:
 a) Change this:
//$open_SSL_pub="-----BEGIN PUBLIC KEY-----
//... copy & paste your public key
//-----END PUBLIC KEY-----" ;
to this, with your public key:
$open_SSL_pub="YOUR PUBLIC KEY" ;

 b) Change this:
//$open_SSL_priv="" ;
to this, with your private key:
$open_SSL_priv="YOUR PRIVATE KEY" ;

 c) Change $DKIM_d='example.com' ; to contain your domain

 d) Change $DKIM_s='test' ; to contain your selector

Rename dkim-cfg.dist.php to dkim-cfg.php

Copy dkim.php and dkim-cfg.php to ListMailPRO folder

Modify ListMailPRO:

*** admin.php Line 827-829 ***

// domail!!!
require('dkim.php'); // DKIM MOD
function domail($sendq='',$sendt='',$xid='',$batch){

*** admin.php Line 1387+ ***

     $header .="X-LMP-Recipient: $email";

     // BEGIN DKIM MOD
     if($smtpsend) $header .= "$crlf$crlf";

     if(($htmsg && $htmail && !$textonly) || $fatt){
      $body = "This is a multipart message in MIME format.$crlf$crlf$body";
     }
     /* above changes were needed because we had incorrectly appended the 'multipart' string to the header not the body, which affected DKIM signing the proper body length with HTML mail */
     // END MOD

     if($timedebug) $time = mtime() - $stime;

*** admin.php Line 1695+ ***

       // data - both send methods
       if(!$error){
        // start data
        // BEGIN DKIM MOD
        $header = str_replace("\r\n","\n",$header);
        $header = str_replace("\n","\r\n",$header);
        $body = str_replace("\r\n","\n",$body);
        $body = str_replace("\n","\r\n",$body);
        $dkim = AddDKIM($header,$xsubj,$body);
        $header = $dkim.$header;
        $body = str_replace("\r\n.","\r\n..",$body); 
        $themesg = $header.$body;
        $xmsg = str_replace('<','&lt;',$themesg);
        $xmsg = str_replace('>','&gt;',$xmsg);
        // END MOD

        if($smtp_debug) logwrite($bugf,"> SENT DATA\r\n");