One-Click Unsubscribe Header Builder
Produces both headers (List-Unsubscribe with mailto: and https:, plus List-Unsubscribe-Post: List-Unsubscribe=One-Click) that Gmail and Yahoo require for senders above 5,000/day.
List-Unsubscribe: <mailto:unsubscribe@example.com>, <https://example.com/u/abc123> List-Unsubscribe-Post: List-Unsubscribe=One-Click
Endpoint must respond 200 to a bare POST with no body. Test with: curl -X POST https://example.com/u/abc123
Builds the two headers from your unsubscribe endpoint URL. Validates that the endpoint accepts POST (one-click requires POST, not GET).
Any bulk sender hitting 5,000/day to Gmail or Yahoo. Required since February 2024. Without it, mail goes to spam regardless of other config.
FAQ
Why does Gmail require POST and not just a URL?+
POST prevents prefetchers (link scanners, security tools) from accidentally unsubscribing users. The user must explicitly click to trigger the unsubscribe.
Do transactional senders need this?+
No. The Gmail/Yahoo bulk-sender requirements apply only to senders categorized as bulk (5,000+/day to that provider's users).
Keep going
Articles, glossary entries, and other tools on the same topic.
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Verify on a real sendNate built Outsolvi after watching every email-tracking tool he had ever used lie to him about opens. Outsolvi runs Tier 1 to 5 confidence scoring on every open, native in Outlook and Gmail, so the number on the dashboard is one a rep can actually act on.
We update these pages when the underlying mechanics change — new mailbox-provider rules, new tracker behavior, new measurement gaps. The dates above are real revisions, not auto-touches.