In the war against malware on the web, messenger services like Facebook messenger and google chat have been known to visit links passed through their service. the attacker hijacks an account, and then sends the malware link to all of that users contacts. coming from a trusted source, those contacts visit the link, and they get their account hijacked, and the cycle continues. in order to combat this, the platforms will visit the link to verify it isn't malware. Thus, the platform has the magic url. We trust them not to abuse this privilege, but that's one case where someone other than the intended recipient has the magic url.