uilicious/inboxkitten ? reverse-engineered prompt

Build me a simple disposable email website like Inboxkitten.

I want people to be able to visit the site, pick a temporary inbox name, and instantly see emails sent to that address in the browser. The inbox should update when new mail arrives, and the whole thing should feel lightweight and easy to use.

Make it something I can run locally with Docker and also deploy with Mailgun using environment variables for the email domain, API key, and site domain. If there are any setup details I need for Mailgun routes or receiving mail, please include clear instructions in the README or setup notes.

Keep the design clean and friendly, since this is meant for quick disposable inboxes. If you need current Mailgun or deployment details, look them up online before wiring it up.