A feedback loop (FBL) is a service offered by some mailbox providers that tells a sender whenever one of their recipients marks a message as spam. When a subscriber hits “report spam” at a participating provider, the provider forwards a copy of the complaint back to the sender. This lets you find the complaining address and stop mailing it, which protects your sending reputation before more damage is done.
How it works
You register your sending domains or IP addresses with a provider’s FBL program (for example, through a signup form or via ARF-formatted reports). When a recipient marks your mail as spam, the provider sends you an Abuse Reporting Format (ARF) message. Your email platform parses that report, identifies the address, and adds it to a suppression list so it never receives mail from you again. Not every provider offers a public FBL, and some (notably Gmail) share aggregate complaint data through postmaster tools rather than per-message reports.
Why it matters
Spam complaints are one of the strongest negative signals in email deliverability. A rising complaint rate tells inbox providers that people do not want your mail, which pushes future sends toward the spam folder. Acting on FBL reports quickly keeps your complaint rate low and your list clean.
Applied to B2B quoting on Shopify
If you send quotes, follow-ups, or expiry reminders from your own domain, a buyer who marks one as spam can quietly hurt your ability to reach every other buyer. Honoring FBL complaints (and pairing them with proper SPF, DKIM, and DMARC) keeps quote emails landing in the inbox where they can be opened and accepted. See the B2B quoting glossary for related deliverability terms.