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I'm using Email tracking services of some Email sender company. It is achieved through requesting img resource when opening email. Here is the code inserted into HTML message:

<img src="https://ci4.googleusercontent.com/proxy/TObr7aARe70s=s0-d-e1-ft#http://www.mywebsite.com/TrackEmail?j=eyJ1IjoiMQ4In0%3D&amp;r=0.614693022798747.gif" width="2" height="1">

I'm interested in how eventually the request will come to my website. Can anyone please explain me? I think the magic is somewhere in this part ...d-e1-ft#htt....

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up vote 1 down vote accepted

If you are looking at this email in Gmail, I believe that the googleusercontent.com was added to your image. Google recently announced that they are now caching all images shown in Gmail on their own servers as a user privacy protection.

This may break some email tracking. It will certainly limit the amount of information you can gather about Gmail users that open emails. You will no longer be able to see what browser they use, for example.

The announcement article gives some more information about how the Google image proxy actually works. Google serves the images from their site, but has their server request it from your server the first time it is used.

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Thanks for your comment, Stephen! So what you're saying is that my original email contained only this part - mywebsite.com/…, but then google itself added the first part? – Maximus Jan 5 '14 at 16:36
I guess you're right. I've found the same approach for Yandex (russian mail service) - src="https://cache.mail.yandex.net/mail/edd41c3205985a91959aca6e6924c3d5/www.i‌​nreado.com/TrackEmail?j=eyJ1IjoiMzdDND... – Maximus Jan 5 '14 at 17:34
So basically caching doesn't break basic tracking system. However, I don't understand how they can track if certain email was opened second time? I assume that google wouldn't make second request to my server for the image since it's already cached. – Maximus Jan 5 '14 at 17:37
It would break tracking of second open. – Stephen Ostermiller Jan 5 '14 at 22:33
Yes, that's what I thought. But they can show me statistics about the consequent opens, any ideas on how they manage to track that? – Maximus Jan 6 '14 at 7:22

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