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We are going through a website redesign that involves changing URL's for the pages on our site. Currently all our pages are in the format domain.com/example.html and we are moving to stip off the .html file extension so it would just be domain.com/example We have thousands of pages as the site deals with news so building a redirect for each individual page isn't really feasible. My plan is to have a generic rewrite rule that redirects any page that ends .html to the stripped off version of this. A problem I can see with this is that it will also redirect pages that don't exist. So for example, domain.com/non-existant-page.html would 301 to domain.com/non-existant-page which would then return a 404 status. What would the SEO repercussions be for this? Obviously if a page doesn't exist already then it shouldn't show up in the search engine indexes and shouldn't be a problem but I'm a bit worried about how old pages that currently legitimately 404 will be treated when they start to 301 redirect to a 404 instead. Not sure if there any other potential issues from this that I've missed either? Thanks!