What Is a Feedback Loop (FBL) and What Is a Spam Complaint Rate?

A feedback loop (FBL) is an arrangement in which a mailbox provider notifies a sender each time one of its users marks a message from that sender as spam. The report arrives as an email in Abuse Reporting Format (ARF) containing the original headers, so the sender can identify the recipient and stop mailing them. The spam complaint rate, the share of delivered messages that were reported, is the number these reports feed, and it is one of the strongest reputation signals in email.

Quick summary

• The sender registers its sending IPs or DKIM domain with the provider FBL program.
• A recipient at that provider clicks Report spam on a message.
• The provider generates an ARF report and emails it to the address registered for the FBL.
• The sender parses the report, finds the recipient (often via a unique Return-Path or a List-Unsubscribe token) and unsubscribes them.
• The complaint is also counted against the sender reputation, whether or not the FBL exists.

How a feedback loop works

1. The sender registers its sending IPs or DKIM domain with the provider FBL program.
2. A recipient at that provider clicks Report spam on a message.
3. The provider generates an ARF report and emails it to the address registered for the FBL.
4. The sender parses the report, finds the recipient (often via a unique Return-Path or a List-Unsubscribe token) and unsubscribes them.
5. The complaint is also counted against the sender reputation, whether or not the FBL exists.

Who offers feedback loops

• Yahoo (including AOL): the Complaint Feedback Loop, keyed on your DKIM d= domain.
• Microsoft (Outlook.com, Hotmail): the Junk Email Reporting Program (JMRP), keyed on sending IPs.
• Comcast, Fastmail, Mail.ru, Seznam and several others run similar programs.
• Gmail does not send per-message reports. Instead, Google Postmaster Tools shows an aggregate spam rate for your domain, and the Feedback Loop feature there only works for senders embedding a Feedback-ID header on high-volume campaigns.

Example: what an ARF report contains

From: feedbackloop@provider.example
Subject: complaint about message from 203.0.113.10
Content-Type: multipart/report; report-type=feedback-report

Feedback-Type: abuse
User-Agent: ProviderFBL/1.0
Original-Mail-From: <bounce+a1b2c3@yourdomain.com>
Arrival-Date: Sun, 12 Jul 2026 09:15:40 +0000
Reported-Domain: yourdomain.com

[original message headers, recipient address usually redacted]

Complaint rate: the numbers that matter

Gmail asks bulk senders to stay below a 0.10% spam rate and never above 0.30%, measured in Postmaster Tools as spam reports divided by messages delivered to the inbox. Yahoo applies a similar threshold. At 0.3% that is three reports per thousand delivered messages, a level that a legitimate list reaches quickly if it includes people who never signed up, or if unsubscribing is harder than clicking Report spam.

How to keep complaints low

• Make unsubscribing one click with List-Unsubscribe and List-Unsubscribe-Post headers, and honour it within two days.
• Use a recognisable From name and the same domain every time so people know who you are before they read.
• Send only to addresses that opted in, and drop anyone who has not opened in many months.
• Never send marketing to a customer support thread or to addresses harvested from invoices.
• Keep transactional mail transactional; a receipt with a promotion attached invites reports.

Feedback loops and OquMail

For a small business sending from OquMail mailboxes and the transactional send API, complaint volume is normally tiny because the mail is expected. If you run newsletters, use a dedicated subdomain and a tool that processes FBL reports, and keep your primary domain for conversations and receipts. The OquMail delivery log shows you rejections and deferrals per message, which is where a rising complaint rate first becomes visible as throttling at a specific provider.

What to do with each report

Treat an ARF report as an unsubscribe plus a warning. Remove the recipient immediately, then look at what the message was: if the same campaign generates several reports in a day, pause it and check how those addresses were collected. A single complaint on a receipt usually means the wrong address was entered at checkout, which is worth correcting in your customer record rather than ignoring.

Common questions

Do I need to sign up for feedback loops myself?

Only if you operate your own sending IPs or bulk platform. Hosted providers and newsletter services register on your behalf.

Is a complaint the same as an unsubscribe?

No. An unsubscribe is neutral. A complaint tells the provider the message was unwanted and damages reputation. The goal is to make unsubscribing so easy nobody chooses the spam button.

Does a reply count as positive feedback?

Yes. Replies, moving to the inbox, and adding to contacts are strong positive signals at the major providers.