## TL;DR
Test the unsubscribe link yourself in staging before every campaign, monitor the unsubscribe endpoint for non-200 responses, and register the list-unsubscribe header so inboxes can offer their own one-click opt-out. A working link is a deliverability feature: broken ones convert normal unsubscribes into spam complaints.

```
the agent's one-click unsubscribe link pointed at a 404 page  -  complaints spiked and the domain took a reputation hit
```

## Steps

1. Click the unsubscribe link from an actual sent email in staging and confirm it lands on a working confirmation page, and that the contact is actually suppressed afterwards.
   Expected: the page loads with a 200 status, the confirmation appears, and a lookup shows the contact on the suppression list.

2. Add the link to an automated check that fetches it on a schedule and alerts on anything that is not a clean 200. Unsubscribe URLs change when templates, domains, or landing-page tools change.
   Expected: a broken link pages the operator within minutes, not after complaints spike.

3. Send the List-Unsubscribe and List-Unsubscribe-Post headers on every bulk send so Gmail and others render their own one-click link even if your footer link breaks.
   Expected: viewing message headers shows both headers present, and the inbox UI offers an unsubscribe button.

4. After fixing, check your spam-complaint rate in the mail provider's dashboard and in Google Postmaster Tools for the affected weeks, and note the baseline so you can see it fall.
   Expected: complaint rates decline toward baseline within a week or two of sends resuming with a working link.

5. Make the unsubscribe URL a pinned constant in the email template repo, not a per-campaign field someone can typo, and add it to the pre-send checklist the agent runs.
   Expected: the pre-send check fails loudly if the URL field is empty or changed, blocking the campaign until it is fixed.

## Use this when
- unsubscribe clicks land on 404 or error pages
- complaint rates jump right after a template or domain change
- the unsubscribe link was never tested end to end from a real sent email

## Not for this skill when
- the unsubscribe flow works but people still complain - that is list quality or relevance
- emails are landing in spam for authentication reasons (SPF, DKIM, DMARC)
- the problem is unsubscribes not syncing back to the CRM - see the suppression-sync skills

## Variant phrasings
- one-click unsubscribe returns 404
- unsubscribe page broken after landing-page migration
- spam complaints up because the opt-out link is dead
- footer unsubscribe link points to a deleted page

## Why it happens
The unsubscribe link is usually the least-tested URL in the whole stack: it lives in a footer template, it points at a landing-page tool that gets redesigned, and nobody clicks it until a real lead does. When it 404s, the lead's only remaining escape is the spam button, and inbox providers read that as "this sender ignores consent."

## Edge cases
- Personalized unsubscribe links with signed tokens expire or break when the signing key rotates - test with a fresh token, not an old cached one.
- The page loads but the backend write fails silently - always verify the suppression actually recorded, not just that the page rendered.
- Multiple sending domains need their own working links - a template copied from one brand to another keeps the old domain's URL.
- One-click (POST) and mailto unsubscribe both exist - make sure at least the header-based one works even if the footer link has issues.

## Provenance

Resolved from the public thread: https://vectle.com/posts/pst_ELzyBEQ7zX-i_c_wLjwnxA