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Comment by renewiltord | Hacker News Reader

Tracking pixels don’t even work with Gmail because Google fetches them out of band. It doesn’t reveal open rates.

True, but HSBC thinks you read the email, because somebody fetched the tracking pixel, right? The irony is that HSBC and others who use this kind of thing probably aren't in the least interested in when or how many times you open the email. Whoever came up with this idea (probably) really did think it was (just) a pretty good way of figuring out if they have your correct email.

They do work for the inferred purpose here though, assuming Gmail only downloads them when the email is successfully delivered to the mailbox (and thus the address is valid).

IIRC, google limits their opening of remote images if they're unique per email or from less reputable sources.

They also send you an email back saying your email wasn't delivered after a few days or hours, so there's little benefit in using the tracking pixel to determine if an address exists.

Don't know if they fetch images from emails sent to non-existent addresses, but I would if I were to design such a system.

> Gmail because Google fetches them out of band. It doesn’t reveal open rates.

"Our open rates have skyrocketed! send more emails!"

What do you mean by 'fetches them out of band'?

It downloads them and stores in serverside cache before you ever open the email

Frankly the best outcome as it makes them useless.

That does mean the email address exists though which was what HSBC was questioning.

Same with Apple Mail

Apple's system doesn't work. At least not for everyone. https://www.grepular.com/Apples_Protect_Mail_Activity_Doesnt...

I mean, they still work in some way. If you use tracking pixels to see if an email was read, I agree with you that this break the functionality. But if you just want to see if the email exists, then the fact that google fetches them (and triggers the parametric URL) still tells you something

It would be better if google also fetched tracking pixels in emails sent to addresses that do not exist.

So, why use a tracking pixel for that? Just send an email. e.g.

    $ head -n 100 /dev/random | md5sum
    a6cc1b7c09ccb122cb066c89e16b3140  -

And that yields an instantaneous error message https://i.imgur.com/twHhIU3.png that reads "Address not found. Your message to a6cc1b7c09ccb122cb066c89e16b3140@gmail.com was not delivered because the address could not be found".

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