Complaint rate alerting at threshold of 0.1% or less

Google's 2024 bulk sender guidelines mandate that senders maintain complaint rates below 0.10% to avoid inbox filtering at Gmail — the platform receiving roughly one-third of all consumer email in the US. Complaint rates above 0.30% result in throttling or blocking. Without code that monitors this rate and fires an alert before crossing the threshold, the first indication of a problem is often a sharp drop in open rates, by which point Gmail's filtering is already active and may persist for days or weeks after the rate is corrected. The 0.08% early-warning threshold gives an action window before the hard limit is breached.

Compute complaint rate over a rolling 24-hour window and fire alerts at two thresholds — a warning at 0.08% (pre-threshold) and a critical at 0.10% (Google's hard limit). Run this check from a scheduled job or after each FBL event batch:

const COMPLAINT_RATE_WARNING  = 0.0008  // 0.08%
const COMPLAINT_RATE_CRITICAL = 0.001   // 0.10%

export async function checkComplaintRate(domain: string): Promise<void> {
  const since = new Date(Date.now() - 24 * 60 * 60 * 1000)
  const [sent, complaints] = await Promise.all([
    db.emailLog.count({ where: { fromDomain: domain, sentAt: { gte: since } } }),
    db.complaintEvent.count({ where: { domain, receivedAt: { gte: since } } })
  ])
  if (sent === 0) return
  const rate = complaints / sent
  if (rate >= COMPLAINT_RATE_CRITICAL) {
    await sendAlert({ severity: 'critical', message: `Complaint rate ${(rate * 100).toFixed(3)}% for ${domain} — above Google's 0.1% limit` })
  } else if (rate >= COMPLAINT_RATE_WARNING) {
    await sendAlert({ severity: 'warning', message: `Complaint rate ${(rate * 100).toFixed(3)}% for ${domain} — approaching threshold` })
  }
}

Persist the computed rate to DomainReputation.spamRate so the check feeds the trend graph alongside Postmaster Tools data.