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Image Caching in Web Email Clients – Alarm for your Email Metrics?

March 21, 2018 / Kevin George

Recently Yahoo! Mail announced that they have changed how they handle embedded images in emails. Similar to the bold move by Gmail in 2013 to adopt image caching, Yahoo! will now cache all the images and display them from their own proxy servers. Webmails like Gmail and Yahoo! implemented this to greatly improve email load speed and reliability, but it throws a monkey wrench into the works for email marketing. This is how the tracking codes work. When your subscriber opens an email and enables images, a request to download all the linked images is sent to the server and a tracking pixel is downloaded along with rest of the images. The request sent to the server is called HTML referrer and it is the code after the URL that contains information about your subscriber such as device id, IP address and email client used.