I needed to communicate with an iframe on Sharepoint, however Sharepoint returned Load denied by X-Frame-Options … To override this limitation you have to create a Webpart page where you’ll add the code <WebPartPages:AllowFraming runat="server" /> into the <asp:Content> section (that might work somewhere else, but I did this way).
You can also add it into your masterpage to allow it everywhere on your website. Add it into your <head> block:
Now you can use postMessage() to communicate with your iframe.