Apple Mail Privacy and open tracking
Mail privacy features can inflate raw open counts. Use the is_prefetched field and non-prefetched metrics to distinguish likely machine activity from other opens.
What changed
Open tracking embeds an image in each message and records an open when a mail client loads it. Apple Mail Privacy Protection can prefetch message images without the recipient reading the message. This image load still creates an open event.
As a result, raw open counts can include machine activity and should not be treated as a precise measure of human engagement.
Non-prefetched opens and likely machine opens
Bird distinguishes non-prefetched opens from likely machine opens. Each open event has an is_prefetched field. The dashboard open rate uses non-prefetched opens, while the raw counts remain available. See open and click tracking for the calculation.
Filtering does not make opens exact. Recipients who block images or use text-only clients can read a message without registering an open.
How to read engagement now
Treat opens as a soft signal: good for spotting trends and large relative differences, unreliable as an absolute measure or for per-recipient decisions.
- Use clicks, replies, and conversions. These signals provide stronger evidence of engagement than an image load, though automated link scanners can also generate clicks.
- Compare like with like. Open rates are still useful relatively (this month vs last month, variant A vs variant B) as long as the audience mix is similar, since the same share of machine noise affects both sides.
- Don't prune your list on opens alone. Include durable signals such as clicks, replies, or purchases and choose an inactivity window that fits your sending cadence.
Next steps
- Open and click tracking: how opens and clicks are instrumented and how the rates are computed
- Events and webhooks: the per-recipient event definitions, including the is_prefetched flag on open events