How does Gmail’s image caching affect open metrics in HubSpot?

Last updated: March 26, 2018

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Around January 2014, Gmail made some changes to the way they handle images, and this change affected how HubSpot and other Email Service Providers track data about email opens.

Here's how HubSpot reports on open events:

  • To report email opens, HubSpot places a tiny tracking pixel (1px image) in every email you send.
  • When someone opens your email, the images in that email are loaded (including the tracking pixel).
  • This gives us your opened metrics.

So what’s changed? 

Previously Gmail would load images in much the same way as other email clients. However, Gmail changed their services to do the following:

  • Download and cache images on their servers (including the tracking pixel used by HubSpot).
  • It then serves these same images to everyone, irrespective of device type.
  • This affects opens in Gmail’s Webmail client and their Gmail mobile apps (iOS & Android).
  • The result is we are unable to tell whether the open happened on a mobile or desktop device.


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