Detect number of times a particular email has been opened


I've written a newsletter control panel in PHP and a few thousand emails are sent every month from it. The control panel shows if an email was opened, what date/time and what link was clicked. The open date and time are done using the 1 pixel image trick.

I'm wondering if it's possible to show the number of times a particular email has been opened. Obviously when it's opened the first time, I'm capturing that information. But if the person saves the email with the downloaded images, how would I see if they've opened it again?

Thanks in advance
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There is no sure way of detecting this. The pixel trick may not work at all, since many email clients block the downloading of images by default, unless the user clicks to download these images.

Even so, you can try setting no-cache headers for the image, that might encourage some clients to download the image again.
Ray PaseurCommented:
The pixel trick works, I would say, "a lot of the time."  And it works best if your image content in the messages is valuable enough to the clients that they set their mail program to receive the images every time.  ConstantContact uses exactly this strategy to report.

But to put it simply, there is no handshake or accountability for email messages, and the number of times a message is forwarded, or re-read is just not in reach.  However you can say this much with authority: The message was opened at least N times and probably several more times.

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kbitAuthor Commented:
Thanks for both your replies. I've done a test on what I currently have and it seems that even if the images are downloaded and saved in the email, every time the email is opened afterwards, the open date and time are being changed. This is great news as I can use this to count email openings.

You're both right though, email statistics are far from accurate and I'm constantly warning people of this fact.
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