Deliverability glossary · Updated 2026-10-27
List-Unsubscribe
List-Unsubscribe is an email header giving mailbox providers a machine-readable way to opt someone out. It renders as the native unsubscribe link Gmail shows next to the sender name.
The header can carry a `mailto:` address, an HTTPS URL, or both. Mailbox providers use it to render their own unsubscribe control in the interface, which is a far more prominent and trusted affordance than a link buried in your footer.
Counter-intuitively, making unsubscribing easy protects you. The alternative action available to an irritated recipient is the spam button, and a spam complaint damages your sending reputation in a way an unsubscribe does not. Every opt-out taken through the header is a complaint you did not receive.
In 2024 Gmail and Yahoo made it a requirement for bulk senders, together with one-click support and a spam complaint rate under 0.3%. Gmail counts you as a bulk sender at around 5,000 messages a day to its users. It moved from best practice to a delivery requirement in a single policy change.
The header must be present on the message itself, which means the sending system needs control over raw MIME rather than only a templating layer above it.
How Raechly handles it
Messages are built as raw MIME, so Raechly controls every header. Campaigns leave List-Unsubscribe off by default: each sender stays far below bulk volume, and a header like that makes one person’s email look like a newsletter. Every cold email ends instead with the company name, postal address and “Reply ‘stop’ and I won’t email again.” Turn a campaign’s Unsubscribe link on and its emails carry the header with one-click support.
Related terms
One-click unsubscribe
RFC 8058 one-click unsubscribe lets a mailbox provider opt a recipient out with a single POST request, no landing page and no confirmation step.
Spam complaint rate
Spam complaint rate is the share of delivered messages recipients mark as spam.
Sending reputation
Sending reputation is the trust score mailbox providers assign to your domain and IP based on complaint rate, bounce rate, engagement and authentication history.
Back to the full deliverability glossary, or read how these pieces fit together in how Raechly protects deliverability.