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Comment by tgb | Hacker News Reader

Off-topic: I thought that tracking email opening was no longer possible in gmail? My memory of it was that you'd insert an image and track whether that was retrieved, but that GMail started caching all images ahead of time for their users so you couldn't tell if/when it was opened. See, eg, [1]. Is that not correct?

[1] https://arstechnica.com/information-technology/2013/12/gmail...

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No, it only caches when they are requested by the user - google acts more like a proxy. Essentially they're preventing the remote server from grabbing HTTP headers/cookies from gmail users but not preventing them from tracking when it is loaded, chronologically.

The google servers download every image, regardless of whether or not the user later opens it or not. So since every image is downloaded, and subsequent downloads come from google cache, the pixel becomes an ineffective way of tracking open rate.

You can only get the image from cache if it's the same URL. You can still vary those between recipients.

But if it's a different URL for each recipient then google will fetch each individual URL, for each email. So every URL will be opened exactly once, by the google fetch that happens when the google server receives the email. The user will fetch the pixel from google cache. So how can you track open rates by pixel download when 100% of pixels are downloaded just one time?

It probably depends on email clients. If a desktop client fetches email direct from smtp then it will probably also fetch the pixel directly. So tracking all downloads after the first (by google) may yield some signal, albeit not for gmail web users.

Try it. The various MSPs I use report to within a minute whether I open an email or not, and they do this effectively on Gmail and other clients as well.

I see no way they could do this besides the tracking pixels they embed in email, which means that google does not prefetch, but I'd be happy to be proven wrong.

Are you sure they download when Gmail receives the email? I'm pretty sure it's on first use.

This is factually incorrect.

At least for the MSPs I use, they report the open time accurate to within a minute whether I'm using Gmail or not. I see no way for them to do this besides tracking pixels embedded in the document, since I don't see any other outside resources.

I configure all my email clients to not display external images and ask for confirmation if a RR is requested.

In the gmail web browser client, that is in the general settings:

(*) Ask before displaying external images

This is possible. We are doing it at https://www.mailtag.io. Shameless plug though.

IIRC they made a specific exception for tracking pixels, because 1x1 are pretty easy to separate from actual images.

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