List-Unsubscribe header missing – how to fix
Your bulk or marketing mail doesn't include a List-Unsubscribe header. Gmail and Yahoo require it for one-click unsubscribe.
Why it matters
List-Unsubscribe tells inboxes how users can opt out. Gmail and Yahoo use it to show a one-click unsubscribe button. For bulk senders, it's required for good treatment and compliance.
How to fix it
Add a List-Unsubscribe header to every marketing/bulk email. Use angle brackets and mailto: and/or an HTTPS URL.
Example: List-Unsubscribe: <mailto:unsubscribe@example.com>, <https://example.com/unsubscribe>
Ensure the URL or mailto actually performs (or leads to) an unsubscribe. Prefer one-click where possible.
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