[staunch]

1. In the HTML email put

    <img src="http://myserver/invisible.gif">

2. Serve up http://myserver/invisible.gif with a process that trickles down an endless GIF image a few bytes at a time.

3. When the connection to the endless GIF dies, call that the "reading" time.

4. If a "reading" time is under some threshold call it "deleted".

That's how I did it a few years ago anyway.

[derwiki]

That's a neat trick. After hearing about Mirapoint, I built a simple proof of concept that uses time-delayed redirects to gauge how long a user has attempted to load an image:

https://github.com/derwiki/redirect_tracker

Like most email metrics, it's lacking -- but this is still -a little- more information, and that goes a long way in email marketing.

[zrgiu_]

i never load images automatically in my emails, and I bet a lot of other people do that too

[derwiki]

If the sender is ReturnPath certified, Hotmail and Yahoo! automatically load images. Those two providers account for a large portion of email on the internet, so there's definitely value in this product.