Open-rate accuracy

Open tracking works by adding a tiny invisible image to the HTML body. When a mail client loads the image, usend records an email.opened event. That makes opens a useful trend, not an exact count. See Open and click tracking.

#What inflates opens

• Apple Mail Privacy Protection. When people use Apple Mail with the feature on (the default for many), Apple loads images in the background through proxy servers, whether or not the person reads the message. Those emails look opened. A large share of consumer mail goes to Apple Mail users, so rates are often high.
• Security scanners. Corporate gateways open links and images to scan them, producing opens (and clicks) without a human.
• Prefetching by some clients and mail apps.

#What deflates opens

• Images blocked by default in some clients; the person reads the message and nothing is recorded.
• Plain-text email, which cannot carry the image.
• Privacy tools that block trackers.

#How to use the numbers

• Compare, do not count. Compare one campaign with another from the same sender. The bias is similar for both.
• Prefer clicks and conversions for results that matter: a click is a clear action. Remember that scanners cause some clicks too, so look for patterns like all links clicked within a second of delivery.
• Do not prune only on opens. Someone who reads in Apple Mail looks active; someone who reads with images blocked looks inactive. Combine opens with clicks and site activity: Audience hygiene.
• Do not run A/B tests on subject lines using opens alone if a large part of your audience uses Apple Mail; use clicks.

#Turn it off when it does not help

Tracking is configured per domain and is off by default. For transactional mail (password resets, receipts), tracking adds little and can hurt deliverability. Leave it off there, and turn it on only for the domains you use for marketing. Use separate subdomains if you want different settings.

#What usend records

The email.opened event includes the user agent and IP address of the request. An Apple proxy shows up as an Apple address, which tells you the open may not be human. Events arrive through webhooks so you can filter them yourself.