I was looking through my router's logs and came across an intentionally-dropped outbound packet from an office PC. This alone isn't unusual, seems that browsers tend to fire off at least one last packet to a closed connection to a web server and routers will drop those from getting onto the wan.

The IP in this case was 72.21.81.200. It's a Verizon IP. For the heck of it I tried to connect to it (https) and got a browser warning (SSL_ERROR_BAD_CERT_DOMAIN). 72.21.81.200 uses an invalid security certificate.

I looked at the details - hmm. I see dozens of microsoft-related domains. A little bit more digging about the IP:
AS15133 EdgeCast Networks, Inc. d/b/a Verizon Digital Media Services

I don't know. Maybe there's "nothing to see here". I just find it strange that a server serving up content associated with those domains wouldn't be doing so from an actual Microsoft IP. As to why the certificate is invalid, I'm not sure. Is this expected behavior when you hit a HTTPS server on it's IP?