Why do Gmail and Outlook handle images differently?
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They've made different decisions about the tradeoffs between security, privacy, and user experience, and those decisions have changed over time.
Gmail routes images through its own Image Proxy for security scanning and to mask users' IP addresses. For Gmail.com (webmail), images load automatically by default. The proxy is always active. You get consistent tracking behavior, but the data comes from Google IPs, not your subscribers' IPs, and images get cached.
Outlook is more complicated because "Outlook" covers several different products with different behaviors. Outlook.com (webmail) often loads images automatically and doesn't use the same aggressive proxy as Gmail. Outlook desktop application (the one that came with Office, built on the Word rendering engine) historically blocked images by default and required manual "Download images" clicks. More recent Outlook versions have moved toward automatic image loading, but behavior varies by version, organization IT policy, and whether the sender is in a trusted contacts list.
The practical effect: Gmail tracking data is proxy-filtered but fairly consistent. Outlook desktop users who haven't clicked "Download images" show zero opens in your analytics even if they read every word. That's a real problem for B2B senders where Outlook desktop is common.
Knowing your audience's email client breakdown matters here. If you have significant Outlook desktop traffic, your open rate is probably understated for that segment. Click rate becomes more important as a signal for those audiences.
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