PHP send email upon leaving a page

Can someone point me in the correct direction on finding out how to send out an email when/if a person leaves a website.
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Ray PaseurCommented:
No, nobody can do this.  There is no signal when someone "leaves a web site."  The way all of this WWW stuff works is predicated on the HTTP client/server protocol, and the protocol is stateless.

If you understand the protocol and still believe that it's worth trying, then you can write JavaScript that repeatedly calls a script on the server.  Every time it calls, the server updates a database record.  The script also restarts itself and every time it is restarted, it looks at the database record.  If the database record is more than (for example) 20 seconds out of date, it can send the email.

I would not recommend creating a dependency on something like this.  Some of the obvious questions might include, "What if the client visits and then leaves town with the browser open?"  When did the client "leave the website?"  It's just not part of HTTP client/server support.

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