Email Tracking - GMail

Question

I am creating my own email tracking system for email marketing tracking. I have been able to determine each persons email client they are using by using the http referrer bu

Answer 1

Are your images requested with HTTP or HTTPS?

If so, that's the problem.

HTTPS->HTTP referrals do not leak a Referer Header (HTTP_REFERER).

If you embed a HTTP hosted image in an email that is requested from an HTTPS page, it won't send a referrer. (HTTP pages requesting HTTPS, however, do send a referer).The solution is to embed the image as HTTPS. I've tested it, and sure enough, secure HTTPS images do indeed send the Referrer.

One way Gmail could block the referrer information on loaded images by default is if they used a referrer policy, which is supported on most modern browsers. (As of 2011, they did not implement such a policy.)

See the below screenshot of an embedded image that is generated dynamically with the HTTP REFERER of the request: