HubSpot has made a change that will increase the accuracy of your open-rate counts in email.
Historically the way email programs have tracked open rates is by embedding an invisible tiny-pixel image into the body of your email. The theory is, when the email is opened the image will load and the loading of that image will trigger the open-count. While this is a good way of measuring many email opens, there are problems with it. For example, some email applications (like gmail) automatically block images from downloading by default. Others don’t accept HTML emails at all. Both situations undercut the accuracy of pixel-based open-tracking.
To improve the accuracy of our open rates, HubSpot has added click-tracking to the standard pixel-based open tracking within emails.
How Does it Work?
Automatically – but here are the details: When an email is opened, HubSpot will look for the pixel-load as usual. If that pixel doesn’t load, but the recipient clicks a link within the email, it will still count as an open.
How Do We Prevent Double-Counting Opens?
HubSpot bases its counts on individual events like recipient, campaign id, or event type, so even if there are two opens or a pixel-load and a click, the open won’t get double counted.
Source : HubSpot