What is a pixel block and how do privacy settings affect it?
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A tracking pixel is a tiny invisible image embedded in your email. When an email client loads it, the request gets logged and you record an open. A pixel block is what happens when an email client refuses to load that image, or loads it in a way that prevents your tracking server from seeing the request.
Pixel blocking happens in a few ways. Some email clients have images disabled by default and only load them when the reader explicitly clicks "Load images." If images stay blocked, no pixel fires, and you don't see an open even if the person read every word. Older versions of Outlook and many corporate email clients did this.
Then there's the opposite problem: Apple Mail Privacy Protection pre-loads images through Apple's own proxy servers. The pixel fires, you record an open, but you get no IP address or location data, just a signal from Apple's servers. This inflates open counts while reducing the quality of the data you get.
Other privacy tools work differently. Browser extensions like uBlock Origin (for people reading email in webmail) can block pixel requests. Some corporate privacy configurations prevent any image loading at all. DuckDuckGo Email Protection strips tracking pixels from emails before they reach the inbox.
The practical result: your open data has noise in both directions. Some real opens aren't recorded (pixel blocked). Some non-opens are recorded (proxy pre-loading). Click data remains your best signal because clicks are harder to fake in either direction. If you want a realistic picture of engagement, track clicks and conversions more than opens.
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