On this page
Understand feedback loops
What a feedback loop is, the complaint-rate threshold to stay under, and how it protects your delivery.
A feedback loop (FBL) is a data stream from an inbox provider that passes their users' spam complaints back to the sender. MailMachine processes those complaints automatically, removing or unsubscribing the people who complained so you don't email them again - which protects your delivery.
Why feedback loops matter
Feedback loops let providers track how many complaints a sender generates and act on it. A sender who generates lots of complaints causes real delivery problems, especially on a shared IP where it affects everyone in the pool.
The number to watch
A complaint rate above 0.25% (1 in 400) to any one provider, on any one send, is considered a problem. Stay under it.
Where complaints can come from
You can filter complaints (FBLs) by provider in your delivered campaign's contact activity. Most major inbox providers run feedback loops - Microsoft and Outlook/Office 365, Yahoo, AOL, Comcast and Verizon among them - alongside a long list of international and niche providers. Gmail is the notable exception: it reports through Google Postmaster Tools rather than a traditional feedback loop.
Best practice
- Keep complaint rates under 0.25%.
- Let MailMachine remove complainers automatically.
- Use double opt-in so subscribers actually want your mail.
- Watch for patterns and keep your list clean.
The impact of high complaints
Left unchecked, high complaint rates lead to blocked mail, worse inbox placement, damage to a shared IP's reputation, and in serious cases account suspension or blacklisting.
Troubleshooting
Complaints suddenly rose - look at the campaign that triggered them, check whether your subject style or sender name changed, and see if old or unengaged contacts crept back in.
No FBL data for some providers - not all run feedback loops; Gmail uses Postmaster Tools, and some only report to the platform rather than individual senders.
Complaints high but content seems fine - confirm subscribers remember opting in, check your frequency hasn't crept up, and run a re-engagement campaign.
Reducing complaints - make unsubscribing easy and obvious, set clear expectations at signup, segment for relevance, and remove inactive subscribers regularly.
For the broader metric, see Bounces, complaints and unsubscribes.