Tenseg LLC

This plugin will look at another site you specify whenever a 404 error occurs and check if the requested path is there. If the path is found, it will redirect there rather than show the WP 404 page.
This is particularly useful to silently redirect over to an archival copy of a website when a major redesign has been done.
More information about this plugin can be found <a href="https://www.tenseg.net/software/404sitechecker" rel="nofollow ugc">on its homepage</a>.

404 Site Checker

When you get a 404 this will check the requested path at a site you define and redirect there if found rather than showing the 404.

Brad Parbs

surfboards

Quickly output a 404 for static files that aren’t found, rather than loading the normal 404 page.
Any static files ( images, text, pdfs, etc ) that don’t exist will 404 as soon as possible, rather than loading the entire WordPress application.
<h3>Details</h3>
By default, the list of extensions to check are the results of <code>wp_get_ext_types</code>, but can be filtered with <code>static_404_extensions</code>.
The output is a static page with the text <code>404 Not Found</code>, this text can be edited by filtering <code>static_404_message</code>.
A 404 status code will be used, but can be filtered with <code>static_404_response_code</code>.
Passing true to <code>static_404_should_process_request</code> will short-circuit and skip processing the request. This filter gets passed the current request.

Static 404

A WordPress plugin to quickly send a 404 for missing static files.

404 Site Checker vs Static 404