Additionally, you can use .htaccess to use custom error pages that are not .shtml only.
Code:
ErrorDocument 500 /errors/500.php
ErrorDocument 404 /errors/404.php
ErrorDocument 403 /errors/403.php
ErrorDocument 401 /errors/401.php
ErrorDocument 400 /errors/400.php
Simple add some or all of these lines into your root [public_html] .htaccess file and it will be reflected across your entire site.
This is useful if you want to use something like PHP to put the error message into a database so you can see where the bad links are coming from, or something like that.
