FBL processing automated

A feedback loop (FBL) complaint fires when a recipient hits the 'Report Spam' button in their email client — Yahoo, Comcast, and other providers forward these reports to the sender via RFC5965 ARF-formatted emails. ESP platforms (SendGrid, SES, Mailgun) deliver FBL events directly via webhook. If the application does not process these events and add the complaining address to the suppression list immediately, the system will send again to someone who has explicitly marked the email as spam — guaranteeing a second complaint from the same address. Repeat complainers are among the strongest signals ISPs use to classify a sending IP as spam-originating.

Add a complaint event handler to your ESP webhook processor. Every spamreport (SendGrid), complained (Mailgun), or SNS complaint notification (SES) must write to the suppression table immediately:

// In your ESP webhook handler (e.g., src/app/api/webhooks/sendgrid/route.ts)
export async function handleSendGridEvent(events: SendGridEvent[]): Promise<void> {
  for (const event of events) {
    if (event.event === 'spamreport') {
      await db.suppression.upsert({
        where: { email: event.email.toLowerCase() },
        update: { reason: 'fbl_complaint', updatedAt: new Date() },
        create: {
          email: event.email.toLowerCase(),
          reason: 'fbl_complaint',
          source: 'sendgrid_fbl',
          suppressedAt: new Date()
        }
      })
    }
  }
}

Verify webhook signatures before processing (SendGrid sends a X-Twilio-Email-Event-Webhook-Signature header). Persist FBL events to a complaintEvent table in addition to the suppression upsert so complaint rates can be computed per campaign and per domain.