Spam complaint rate
How often recipients hit the junk button, measured differently by each provider. Google wants its metric under 0.3 percent, ideally under 0.1.
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What it is
Roughly, complaint rate is how often recipients hit the junk button on your mail. Precisely, there is no single metric, so always name the source and the denominator. Google Postmaster Tools reports a user-reported spam rate: messages Gmail users marked as spam, measured against the mail Gmail counted as delivered to their inboxes, per day and per authenticated domain. A classic feedback loop from Yahoo, Microsoft, or an access provider hands you individual complaint reports, and any rate you build from those uses your own denominator and covers only the mail that provider received. The numbers are not interchangeable and should never be averaged into one figure.
Google's bulk sender rules draw the line at 0.3 percent on the Postmaster metric on a single day, and tell senders to sit under 0.1 percent in practice. Those are tiny numbers: 3 complaints out of 1,000 is already the ceiling. Your own logs cannot produce them, since a junk-button press happens inside the provider. Watch each source per provider and per campaign, because a blended average hides the one segment that hates you. Every complainer you can identify gets suppressed on the spot, no exceptions.
The counterintuitive part: a hidden unsubscribe link does not reduce complaints, it manufactures them. Someone who cannot find the exit reaches for the junk button instead, and an unsubscribe costs you one address while a complaint damages delivery for everyone on your list. Recovery is slow and lagging too, since the rate is computed daily and reputation takes weeks of clean sending to climb back, so one bad purchased list can poison a quarter.
Ask AI for it
Build complaint rate monitoring for our email program, keeping each metric labelled with its source and denominator instead of blending them. Track Google's user-reported spam rate from Postmaster Tools as its own series (Gmail's numerator, Gmail's denominator, per authenticated domain per day). Separately, ingest complaint events from the provider webhook and from every feedback loop we are registered for, and compute a rate against the messages we delivered to that provider, broken out by receiving mailbox provider and by campaign. Never sum the two into one figure. Suppress any complaining address immediately and permanently. Warn when Google's user-reported spam rate passes 0.1 percent on a single day and automatically pause queued marketing sends when it passes 0.3 percent, applying the equivalent thresholds per provider to that provider's own series, while leaving transactional mail flowing. Store 90 days of history, chart the trend next to unsubscribe rate so we can see complaints rising as unsubscribes fall, and link each spike to the campaign and segment that caused it.