An open is an imperfect proxy
Apple Mail Privacy Protection can hide a recipient’s IP and prevent senders from learning whether messages were opened; remote content can be handled privately. An image request is therefore not a reliable human-reading receipt. [Apple: Mail Privacy Protection]
Match the measure to the message
| Message purpose | Our suggested evidence |
|---|---|
| Customer conversation | A genuine response or recipient-confirmed outcome |
| Account activation | Completed activation, alongside message-delivery evidence |
| Subscribed updates | Opt-in state, unsubscribes, complaints and relevant actions |
| Incident notification | Agreed recipient checks and operational acknowledgement |
These are proposed measurement choices. They are not published filter weights, and none alone proves how all receiving systems classified the message.
Make unsubscribing straightforward
RFC 8058 defines one-click unsubscribe signalling using List-Unsubscribe and List-Unsubscribe-Post, with an HTTPS endpoint and authenticated headers. A visible link in the body alone is not that protocol. Its design distinguishes the unsubscribe action from ordinary URL retrieval. [IETF RFC 8058: one-click unsubscribe]
For subscribed messages, test the entire unsubscribe path and record how suppression reaches each sending application. Keep necessary operational notifications distinct in purpose and governance. See corporate deliverability for the provider-policy context.
Primary sources
Provider requirements and product capabilities can change. Check the linked source before a production change.