Catch Salesforce outbound message and write to file.

Sf.php

<?php
/* joshQ
 * Crude SOAP Responder for SFDC Outbound Messages</u></span>
 * THIS SOFTWARE IS PROVIDED AS IS.*/

// Get raw post data
$data = fopen('php://input', 'rb');
$content = fread($data,5000);

// Write message to file
$fh=fopen('soap.txt','a'); // change location
$stamp = "\n+++ " . date('r') . " : " . time() . " : +++\n";
fwrite($fh,$stamp);
fwrite($fh,$content);
fwrite($fh,"\n---------------------------------------------------\n");
$retVal = fclose($fh);

// Respond
if ($retVal) {
  respond('true');
}else{
  respond('false');
}

function respond($tf) {
  print '<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
                 <soapenv:Body>
                   <notifications xmlns="http://soap.sforce.com/2005/09/outbound">
                      <Ack>' . $tf . '</Ack>
                   </notifications>
                  </soapenv:Body>
                </soapenv:Envelope>';
}
?>