What’s the role of high open-to-complaint ratio?

You've probably heard that low complaint rates are good. But here's the thing mailbox providers actually care about: not just whether people complain, but whether they were engaging in the first place.

The open-to-complaint ratio is exactly what it sounds like. It compares how many people open your emails against how many mark them as spam. A high open rate with almost zero complaints tells providers your list actually wants to hear from you. A low open rate with even a handful of complaints is a much bigger problem than the raw complaint number suggests.

Here's what the numbers look like in practice:

• Healthy: 25%+ open rate, complaint rate under 0.08%. That's the kind of signal that builds sender reputation over time.
• Caution zone: 15-25% opens with complaints creeping toward 0.10-0.15%. Some people are engaging, but others are clearly done with you.
• Danger zone: Below 10% opens and any complaints above 0.10%. At that point, you're sending to an audience that's either ignoring you or actively reporting you.

For context, Gmail uses its Postmaster Tools to track complaint rates, and they've stated publicly that rates above 0.10% start to affect delivery, with 0.30%+ causing serious inbox problems. A complaint rate under 0.08% is their stated comfort zone. But those thresholds hit harder when your open rate is already low, because it means a larger share of your actual audience is complaining.

Why does the ratio matter more than complaints alone? Imagine two senders. Sender A has a 5% open rate and a 0.05% complaint rate. Sender B has a 40% open rate and a 0.05% complaint rate. Same complaint percentage, completely different story. Sender B's audience is clearly engaged. Sender A's audience is mostly ignoring them, and the complaints are coming from a pool of people who barely open anything. That's a warning sign about list quality, not just content.

Providers use this kind of signal to distinguish senders whose audiences genuinely want the mail from senders who've just gotten good at suppressing the worst offenders without fixing the underlying problem.

What to actually do if your ratio looks off:

• Segment out subscribers who haven't opened in 90 days or more and stop mailing them regularly.
• Run a re-engagement campaign for that cold segment before you suppress them entirely.
• Check where your complaints are coming from. A spike after a particular campaign is a content or frequency problem. Steady complaints across all sends is a list acquisition problem.
• Make unsubscribing easy. A frustrated reader who can't find the unsubscribe link will hit the spam button instead.

If you want to dig into recovering your sender reputation after a rough patch, that's a natural next step once you've stabilized the ratio. And if your list needs a clean-up before you can even get a clear read on it, we do that too (hi ;)).