That depends entirely on the system in use.
Originally Posted by Samsoske
When a user submits the form, the form processor e-mails or queues the incoming data to be sent later. After that, instead of sending back a response directly, the usual action is to perform a redirect to some resource. This entire sequence is out of your control. It's determined by the service provider.
Your best bet would be to look for documentation about the service you use, or contact the provider for support. However, you might want to first start by modifying
to use an absolute URL. For example,
<input type=hidden name="_thanksurl" value="thankyou.html">
<input name="_thanksurl" type="hidden" value="http://www.example.com/thankyou.html">