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
Record generated. Now make sure it actually passes on real sends.
A correct DNS record on paper still fails 12% of the time at the receiver. Outsolvi watches every send and flags auth failures, opens that look like proxies, and bounces in real time. From $7/user/mo yearly.
Verify on a real sendBuilds the two List-Unsubscribe headers from your unsubscribe endpoint URL, formatted for one-click unsubscribe. Includes the requirement most implementations get wrong: the endpoint has to accept POST, not GET. Header generation only, so test the endpoint itself from your own stack.
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.
Nate 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.