Yesterday afternoon, Copernica disabled file downloads upon the discovery of a security risk by one of our users. The reporting user was able to download random files by manually altering URLs. To prevent abuse, all file downloads were disabled completely on the spot.
When checking their statistics, Copernica users might have noticed a drop in the number of impressions registered for Gmail recipients. At the same time they might notice that the number of unique impressions for these recipients have grown. The reason for this is the new way Google handles incoming emails, using their own servers as a proxy for showing images.
As of recently, Google is rewriting image URLs for incoming emails. When delivered to Gmail, all images in emails are downloaded, cached and then loaded from Google’s servers.
In a nutshell this means:
- You can now only mease unique impressions for email delivered to Gmail
- Gmail now loads images by default
- Copernica is now able to give a more reliable idea of the number of times an email delivered to Gmail is opened
How does Copernica measure impressions?
When a recipient opens an email, the images in the email are downloaded from Copernica’s picservers. Whenever such a download occurs, we call this an impression.
Impressions can give you a rough idea of how many times an email is opened, although this is not an exact estimate because not all users choose to show images in their emails.
Even if you decide to not include any images in your emails, Copernica still inserts an invisible 1x1 pixel.gif to be able to measure an impression. (This of course does not apply for HTML free text versions of emails.)
What changed for Gmail addresses?
To determine if an image is downloaded, it has to be retrieved from our picservers. Obviously it’s not possible to tell how many times an images was downloaded from a third party server.
What Gmail now does however, is:
- Download the image
- Save it to their own cache
- Serve the cached version to its users
According to its blog Gmail does this to protect its users “from unknown senders who might try to use images to compromise the security of [their] computer or mobile device.”
Does this mean I can’t measure impression for Gmail anymore?
No, don’t worry. Whevener a Gmail user opens an email, images are still downloaded from our servers. The fact that this is now done through Google first, doesn’t matter when measuring the number of unique impressions.
For email marketers this does have some consequences though. Rather than downloading email images every time someone opens an email, Google serves the cached versions whenever someone opens an email for the second time. That's why, since recently, it's only possible to measure unique impressions.
Are there any advantages to Gmail’s new policy?
Yes, there are. Before this change in policy, Gmail users had to consciously choose to view email images. And whenever someone just viewed the email without loading images, it wasn't possible to measure impressions.
But because Gmail is now behaving like a proxy, images are now shown by default. And while that’s good news in itself, it also means that Copernica is able to determine the number of unique opens for an email more precisely than before.
My total number of impressions for Gmail is still higher than my number of unique impressions. How is that possible?
It appears that only emails that were received after Gmail started its new policy were affected. For older emails you’ll still be able to see a difference between the total and unique numbers of impressions.
Also, it’s still unknown how long Gmail stores email images on its servers. It is however safe to assume that it won’t be keeping them there forever, because this would result in a massive amount of data the company would have to store, even for their standards. So if there's a significant amount of time between two opens, a new impression might be measured.