FAQ about opens and Gmail caching
I had hoped to blog about something else today, but this still seems to be a big concern for a number of people. There are a lot of questions running around, some of which we don’t have answers to, others of which we have answers based on some evidence.
It’s important to remember that we’ve seen Gmail roll things out and then roll things back and do phased transitions during deployment. What various people are reporting about images and caching and headers are accurate at the time they are tested. But they may not be accurate tomorrow or in a week or in a month.
I’ve also discovered through this process that a lot of different providers use significantly different image tracking in order to record image loads. Some of these techniques seem to be more resistant to Google’s new image loading process than others.
Why is this all so important?
Image tracking has become a fundamental part of email marketing. It’s something that can be measured, and so a lot of marketers evaluate the effectiveness of an email send based partially on open rate.
How does open tracking work?
For open tracking, ESPs inject a uniquely tagged image into the email. When the recipient opens an email and has images on, the email client calls to the sender server and asks the sender server for all the images in the email. When the tagged image is returned to the recipient, the server records an “open.”
How does caching break open tracking?
Caching means that only the first load of an image is provided by the sender’s server. Subsequent loads of an image are served by the caching proxy. Caching proxies are nothing new; they just haven’t affected email enough in the past for us to have to talk about it.
Why are some people reporting zero problems?
The first load of a unique image always happens. Some folks don’t measure repeat opens, so they’re not even noticing any changes in their reporting thus are saying they’re seeing no problems.
What else is image tracking used for?
Image tracking can also be used for device detection by reading the “user-agent” string that each device returns. Gmail is currently rewriting the “user-agent” string thus breaking all device detection. The string is unique enough that it would be possible to tag those opens as “opened through gmail web interface.” Gmail may decide to pass through the user agent in the future, the HTTP standard does allow for that.
Image tracking can also be used for geolocation. Some senders use the location of an IP address to return images relevant to a user’s location. The accuracy of geolocation is totally dependent on the accuracy of the IP to location database used; it is a best guess of the user’s location. Gmail is currently not passing through the user’s IP address when requesting the original image. I don’t expect them to start, given they also don’t reveal user IPs when Gmail web users send mail. This falls in the same category of privacy protection.
Is there a workaround?
I have heard of a few people claiming they have a fix. The problem is all of the fixes I have seen involve doing things that violate the HTTP RFCs. For instance, the “fix” or “workaround” discussed at E-Mail Marketing Tipps is to not send back an image at all. This is working now to track repeat opens, but Gmail may adapt and block this as well. It’s also possible that Gmail may decide people trying to “work around” Gmail’s cache should be blocked outright for violating the HTTP spec.
Where can I find more information?
Other blog posts on the issue, including research on what people have seen.
- Litmus: Gmail Adds Image Caching: What You Need to Know
- Return Path: Google’s Image Caching – Much Ado about Not Much?
- Email Marketing Tipps: Gmail’s image caching: How it affects email marketing & how to heal your opens tracking
- Zettasphere: Google Gmail change Breaks Email Open Tracking
- ExactTarget: Gmail Now Caching Images
- MailChimp: How Gmail’s Image Caching Affects Open Tracking
- EmailExpert: Gmail Breaks Email Marketing Again
- Frenzy Commerce: Gmail image changes: everything email marketers need to know