jfoucher

A very simple plugin that sends the main site administrator an email when one of your visitors encounters a 404 error

Email 404

Send the site administrator an email when someone encounters a 404 error on your blog

JordiPlana

This plugin hooks the normal WordPress workflow in order to determine if the request is processing will cause a 404 HTTP error. In that case it prevents WordPress to do any other processing and sends the user to the page defined in the plugin options.
A working and simple solution.
For more information about this plugin you can check <a href="http://jordiplana.com/404-simple-redirect-plugin-for-wordpress" title="404 Simple Redirect Plugin for WordPress" rel="nofollow ugc">the official page</a>.

404 Simple Redirect

This plugin hooks the normal Wordpress workflow in order to determine if the request is processing will cause a 404 HTTP error.

Email 404 vs 404 Simple Redirect