What is a one-click unsubscribe (RFC 8058)?
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One-click unsubscribe lets someone opt out of your emails with a single action, no landing page, no confirmation step, no "are you sure?" The unsubscribe happens automatically when they click, defined by RFC 8058.
It works through two email headers sent with every message: List-Unsubscribe and List-Unsubscribe-Post. The first tells mailbox providers where to send the unsubscribe request. The second signals that the unsubscribe should happen via a POST request (machine-to-machine) rather than requiring the recipient to click through to a web page.
Why this matters now
In early 2024, Gmail and Yahoo Mail made one-click unsubscribe mandatory for bulk senders. If you send more than 5,000 messages per day to Gmail addresses, you need both headers correctly implemented. Senders without them started seeing spam folder placement increases and delivery rate drops.
The reasoning is straightforward. If someone can't easily leave your list, the next option is the spam button. One-click unsubscribe keeps people off your complaint rate, not off your list (well, both eventually, but the complaint damage is worse).
Does your ESP handle this automatically?
Most major ESPs (Mailchimp, Klaviyo, Brevo, and others) add these headers automatically for qualifying accounts. But "automatic" doesn't always mean "correctly set up." If you've customized your sending domain, moved to a new ESP, or are using a custom SMTP setup, it's worth verifying the headers are there.
You can check your headers directly with our free Email Header Analyzer. Send yourself a test email, grab the raw headers, and paste them in. If List-Unsubscribe-Post is missing, that's your gap.
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