One-click unsubscribe (RFC 8058)
Compliance & List Hygiene · Critical priority · hard-fail gate
What it is
RFC 8058 one-click requires 'List-Unsubscribe-Post: List-Unsubscribe=One-Click' plus an HTTPS List-Unsubscribe URI, and BOTH headers must be covered by the DKIM signature.
How to fix it
Add List-Unsubscribe-Post: List-Unsubscribe=One-Click, include both headers in your DKIM h= tag, and honor unsubscribes within 2 days.
This is a hard-fail gate. If it fails, Gmail / Yahoo / Outlook may junk or reject your mail regardless of everything else — so fix it first.
Check your email
See how your real email scores on this and every other deliverability factor.