Gmail Open Tracking Test at Mailgun
If you haven't heard Gmail has made some changes to the way they serve images in their email clients. They are now caching images on their own servers which should change the data given back to email service providers and marketers since opens are tracked by embedding a tiny image pixel in the email.
We ran a quick test and recorded the results.
The result (at least at Mailgun) is that open events are still tracked and you can get data on the email address that opened the email. However, as to be expected, things like geo-location and user agent strings will show Google's data instead of the recipients' information.
Edit: I also just sent some additional emails and did not actually open them and the data was not returned. So it appears there will not be false positives on opens either.