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Comment by wlesieutre | Hacker News Reader

I'm not clicking an unsubscribe button on something I didn't subscribe to. I have no way of knowing if it will unsubscribe me or if it will tell the sender "Hey guys! This is a real email address! Send him more spam!"

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Clicking unsubscribe isn't the only way to know if the email is good. If your email client loads images then it will be known if you opened the email which will also give your IP, geolocation, device type, client name, user agent, etc.

Depending on your email provider if you mark it as spam that could also be known by the sender if your provider supports the complaint feedback loop.

Here are the docs to see what info is available when sending through mailgun.

https://documentation.mailgun.com/en/latest/api-events.html#...

Most clients don't load images by default. The big providers (gmail and the like) certainly don't.

That's what I've always heard and I can only speak to my personal experience on this, but we track open rates on our marketing emails and have a 36% open rate historically. I'm sure this isn't everyone who is opening them as some percentage have images disabled, but to me this says that a large percentage of our clients do have images enabled as I doubt our actual open rate is tremendously higher than what we are seeing reported.

With Gmail's web interface, it's more complicated than that. Images are loaded by default, but only through a proxy: Google's servers go fetch the image for you and then serve you the image. They only do this once you open the email. So you do leak whether you opened the email, but not your IP address, browser headers, etc. Here's a blog post from 2013 about it: https://blog.filippo.io/how-the-new-gmail-image-proxy-works-...

...or worse: send you to an infected URL and pwn you

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