Very good point. It took us a while to get around that :-)

Perhaps it's simply a poor choice of words on your part, but "get around that" raises red flags for me. It makes it sound like you've found a loophole in their intrusion detection systems, that will (hopefully) be closed when it is detected—which will become ever more likely if your system becomes more popular.

Are you working directly with the providers? If you are not you are basically saying you get around their intrusion detection system in some way?

I think that's a point you should be a bit more transparent about because I'm not sure there are a lot of people who want to risk their google account being locked because of your app. We are all aware of the customer support horror stories dealing with getting your accounts re-enabled after they've been flagged.

Are you keeping log of those services possible address as well? I am not sure what other way you can identify.