How they work

You register your sending domain or IPs with a receiver's feedback loop programme. When a recipient at that receiver marks your message as spam, the receiver sends you a report — traditionally an ARF-format email containing the original message — and you remove that address from your lists. Yahoo, Microsoft, Comcast and most large ISPs run one. Gmail does not: it reports an aggregate spam rate through Postmaster Tools and never identifies the complainer.

Why the rate is what matters

Receivers do not count complaints, they compute a rate: complaints divided by mail delivered to the inbox. Gmail's published ceiling is 0.30% with 0.10% as the target. Because the denominator is inbox deliveries, a low-volume domain can breach the ceiling with a single complaint on a slow day. That is why cold email fleets with many small domains are so sensitive to list quality — there is no volume to dilute a mistake.

What to do with the data

Suppress every complaining address immediately and permanently. Then look at what the complaints have in common — a list source, a segment, a template — because a cluster of complaints is a list problem, not a copy problem. Feedback loop data is also the fastest early warning available: a rising complaint rate shows up a day or two before placement drops, which is enough time to pause a campaign.

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