At least according to the original link, GMail follows the link when a user views an email. That sounds like tracking gold to me. As to masking your IP when yo

At least according to the original link, GMail follows the link when a user views an email. That sounds like tracking gold to me. As to masking your IP when you actually click on the link. How could that possibly work? Your IP is still definitely making its way to the tracking server upon clicking the link. There would be no mechanism for GMail to prevent that unless it rewrote the links to point at its caching server, which would pretty much break GMail. Sure, pre-fetching would create a bit of noise because your IP would be mixed in with the Google IPs, but as you've quite rightly noted, filtering out clicks from AS15169 would eliminate that noise.