You likely want to be able to pass some tracking information about the visitors to your Magento site through to your back-end systems. I usually implement tracking using the same method as Google Analytics, just for convenience. Also, there is a ready-made [URL Builder][1] for clients non-google campaigns. This sends tracking data through to the site but you need a custom module to read those parameters and store them in a cookie. Your order export module can then read the cookie and include that information with the order.

You can intercept a Magento event that is called at the start of every request using this config.xml…

<global>
  <events>
    <controller_front_init_routers>
      <observers>
        <packagename_modulename_observer>
        <type>singleton</type>
        <class>Packagename_Modulename_Model_Observer</class>
        <method>interceptMethodNameCanBeAnything</method>
        </packagename_modulename_observer>
      </observers>
    </controller_front_init_routers>
  </events>
</global>

And then in the method you specify you can…

public function interceptMethodNameCanBeAnything($observer) {
    $request = $observer->getEvent()->getData('front')->getRequest();
    $utm_source = $request->utm_source;

    //do whatever you want with your variable here
}

[1]: https://support.google.com/analytics/answer/55578?hl=en