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
Made it. Now see what happens after you send.
Outsolvi tracks your email once it leaves your outbox: which opens were a person and which were a machine, who clicked, and who replied. Follow-ups stop on their own when someone answers. Outlook and Gmail, from $7/user/mo billed yearly.
Track your next 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 with marketing or promotional mail. Gmail has required it since June 2024. Without it, Google says it may not help you fix delivery problems, and since November 2025 Gmail has been rejecting more mail that misses its sender rules.
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. Google requires one-click unsubscribe only on marketing and promotional messages. Transactional mail, such as password resets and order confirmations, is excluded even when a bulk sender (5,000+/day to that provider's users) sends it.
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 grades every open as a person or a machine, 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.