Sending & delivery events

Complaint (FBL / feedback loop)

A signal from a mailbox provider that a recipient marked your email as spam. Feedback loops relay these back to senders so the address can be suppressed.

How feedback loops work

When someone clicks "Report spam", many providers send a report to the sender through a feedback loop (FBL). Your platform receives it, identifies the recipient, and should stop mailing them immediately.

Gmail doesn’t send per-message reports. Instead it shows your overall spam rate in Postmaster Tools.

Why complaints matter so much

A complaint is the strongest negative signal a recipient can send. Gmail and Yahoo require bulk senders to keep their spam rate under 0.3%, and well-run senders stay under 0.1%. A few complaints per thousand emails is enough to push mail to spam.

Reducing complaints

Only email people who explicitly opted in.
Make the unsubscribe link obvious. People who can’t find it report spam instead.
Use a From name and subject people recognize.
Don’t email contacts who haven’t heard from you in years.

Complaints in MailCraft

Complaints are suppressed automatically, fire an email.complained webhook, and count toward the complaint rate in your reputation score.

Let MailCraft handle the details

Authentication, bounces, complaints and suppression are built in. Start free with 3,000 emails a month, no credit card required.

Start free

Related terms

Full glossary