Does a particular URL exist?A difficult question and one there isn't a general answer to - but you can check whether an http:// URL is readable which is often the question that's being asked. With a URL such as a mailto:, the only way to check whether it exists is to send an email to it and see if you get an answer back from the address owner. You also need to take care with testing like this to ensure that the user can't enter local file URLs on your server and use it to check the existance (or otherwise) of files / directories ....
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