A footer link and one-click unsubscribe are not the same thing
A visible unsubscribe link is part of good user experience, but mailbox-provider one-click mechanisms rely on message headers and a compatible endpoint. The final MIME message generated by the sending platform is therefore the evidence that matters. Template HTML alone cannot prove that one-click support exists.
The endpoint must perform a real suppression action
A technically present header is not useful if the endpoint errors, requires an extra login or fails to suppress future promotional mail. Verification should include a controlled test request and a follow-up check that the address is actually excluded from the intended subscription stream.
Transactional mail needs a different interpretation
Not every message should be treated as a marketing subscription. A receipt or security alert can have different unsubscribe expectations than promotional mail. Classify message purpose before scoring it against promotional requirements instead of applying a single rule to every email generated by a domain.
Test after the ESP modifies the message
Email platforms often add headers after your template leaves the editor. Send a real test message and inspect the raw source. That is the only reliable way to see the List-Unsubscribe and List-Unsubscribe-Post values the recipient actually receives.
Verify the evidence
Use the live analysis that matches this workflow instead of relying on a generic status check.