How fast should FBL complaints be processed?

You sent a campaign, someone hit "This is spam," and their mailbox provider just sent you a report about it. That report is an FBL complaint. A feedback loop (FBL) is a channel mailbox providers use to notify you when a subscriber marks your email as spam. The question isn't just how fast you process those complaints. It's whether your current setup can actually act on them before you send again.

The short answer is: as fast as possible, and almost certainly faster than you're doing it now. The complaining address needs to go onto your suppression list before your next send. A suppression list is simply a list of addresses you never mail again, no matter what campaign or segment they'd otherwise fall into.

If you're sending daily, processing complaints "every morning" means you've already sent that person a second email after they said they didn't want the first. That compounds the damage. A single repeat complaint from someone who already flagged you is a stronger reputation signal than the original complaint was.

Manual vs. automated processing

Manual complaint handling works fine when you're sending a few hundred emails a week. Once you're in the thousands, or sending more than once a day, manual workflows can't keep up. The math is against you.

Automated processing looks like this in practice. Your ESP or sending infrastructure receives the FBL report (usually a forwarded email in ARF format), parses the complaining address out of it, and adds it to your suppression list automatically, without anyone touching a keyboard. Most established platforms do this natively. Twilio SendGrid, Mailgun, Postmark, and Mailchimp all have built-in FBL processing that suppresses addresses in real time or near real time.

And if you're using a platform that doesn't handle this automatically, you'll need to either switch to one that does, or build a lightweight script that ingests ARF reports from your FBL inbox and writes those addresses to a suppression table before each send job runs.

What "fast enough" actually means

Industry guidance from M3AAWG points to under 24 hours as a minimum standard, but that's a floor, not a goal. Real-time or near real-time suppression is better practice for any sender running at meaningful volume.

Think of it this way. If someone complained an hour ago and you're about to run your afternoon batch send, that address should already be suppressed. If it isn't, you're about to make things worse. One extra hit to someone who already flagged you can push your complaint rate over the thresholds that trigger provider-level filtering.

A quick audit you can do right now

• Check whether your ESP automatically suppresses FBL complaints or just logs them for you to action manually.
• Find out how long the gap is between a complaint arriving and that address being removed from your active list.
• Look at your FBL inbox (if you have one) and see whether there are addresses in there that have also appeared in recent sends. That gap is your problem to fix.
• If you're managing this manually, estimate how many sends happen in the time between complaint receipt and your next manual suppression run. That number tells you the risk.

Not sure if your current setup handles this automatically? Our SOS hotline is free and someone will actually look at your specific situation with you. Come find us here.