title: Wordpress - Migrate 404s to different domain
body: <p>Backstory, I've got a "php/symfony web app" that is currently hosted on <code>www.example.com</code> but I'm wanting to have that whole functionality be moved to <code>app.example.com</code> so I can spin up a wordpress site that handles all of the <code>www</code> traffic (its our marketing pages).</p>
  
  <p>The challenge/issue is that we have links in the wild referencing <code>www</code> (ex <code>www.example.com/thing/handled/by/app</code>).  So I need to find a wordpress plugin that will issue 301's for anything it doesn't know how to handle (aka wp needs to have 404 redirect to <code>app</code>).</p>
  
  <p>So if we create a <code>/pricing</code> page in the wordpress site, then its available at <code>www.example.com/pricing</code> and handled by wordpress.  But if someone goes to <code>www.example.com/foo</code> which is not a page wordpress is able to handle, then we have a 301 to <code>app.example.com/foo</code>.  I'm finding some plugins that handle "known" routes but I basically need to have a wildcard redirect but for 404's only.</p>
  
  <p>Let me know if additional details are necessary.</p>