What it is
RFC 8058 defines a POST-based one-click mechanism using List-Unsubscribe and List-Unsubscribe-Post, protected by a valid DKIM signature.
Why it matters
Mailbox interfaces can offer a trusted unsubscribe action without following message-body links, reducing complaints and friction.
How to implement
Provide an HTTPS URI in List-Unsubscribe, add List-Unsubscribe-Post: List-Unsubscribe=One-Click, include both fields in DKIM signing, and process the POST without authentication or user interaction.
Common mistakes
- Redirecting the POST to a login page.
- Using the same token for unrelated subscription scopes.
- Forgetting to sign the list headers.
Verification
POST the specified form body to the delivered header URL and confirm a successful response plus prompt suppression for the intended list.