Hey friends,
This week, we’re digging into one of the most underrated metrics in email: your complaint rate.
Most marketers don’t track it.
Most ESPs barely surface it.
But every major inbox provider? They’re watching it like a hawk.
And if you’re not paying attention—it could quietly crush your deliverability.
Let’s fix that.
📣 What’s a Complaint Rate—and Why It Matters
Your complaint rate is how many people hit the spam button on your email.
Formula:
(Spam Complaints / Emails Delivered) x 100
What that means for you:
< 0.1% → You’re good
0.1%–0.3% → Time to tighten things up
> 0.3% → You’re officially in the danger zone
Even a tiny number of complaints can tank your deliverability—across the board.
🧠 How ISPs Actually Score You
Gmail, Yahoo, Outlook—they don’t care about your campaign names.
They track complaints by:
Sending IP
Domain
DKIM signature
Their scoring is aggregate reputation, not per-send.
So one bad blast to a cold segment can screw up inboxing for everything else.
Your ESP may show campaign complaints, but the ISPs are watching your infrastructure.
🧱 The Blind Spot: ESPs Don’t Show Complaints by Domain
Here’s the problem...
Most ESPs only show you campaign-level complaint stats—and even that’s limited.
What they don’t show?
Complaint rates by domain (e.g., Gmail vs. Yahoo vs. Outlook).
That’s a big miss—because complaint tolerance isn’t universal.
Gmail might tolerate up to 0.3%
Yahoo can be even stricter
Outlook? A black box half the time
If you're seeing dips in inboxing and your ESP isn’t surfacing domain-specific complaint rates, you’re guessing—not diagnosing.
I build segments to help monitor what domains are receiving complaints.
And that’s why Gmail’s Feedback-ID feature is a game changer:
It gives you real-time visibility into where your problems are starting, not just how bad they’ve gotten.
Knowing who’s complaining is just as important as how many.
🔍 New from Gmail: Complaint Rate by Campaign (Yes, Really)
Gmail Postmaster Tools just unlocked a killer feature:
Campaign-level spam insights—if you pass a Feedback-ID header.
Set it up like this:
Feedback-ID: campaignXYZ:userABC:mail789:yourdomain.com
Gmail will:
✅ Group spam complaints by campaign
✅ Show delivery errors
✅ Show inbox vs. spam split
✅ Show auth pass/fail rates
Now you know exactly which sends are hurting you—and which ones are inboxing like champs.
🛡️ How to Keep Complaint Rates Low (and Deliverability High)
Here’s your deliverability defense checklist:
Set up feedback loops for Yahoo, Microsoft, and other ISPs
Monitor Gmail daily via Postmaster Tools
Suppress disengaged subs before they hit “Spam”
Never cold-blast a segment that hasn’t been warmed
Make your unsubscribe link obvious (no one should have to hunt for it)
Watch your complaint trends over time—not just per send
BEFORE YOU GO
Don’t Let Bad Deliverability Tank Your Email Results
If your emails aren’t landing in the inbox, they’re not doing their job. I’ve seen too many brands struggle with deliverability issues without knowing why.
The truth is, a few key optimizations can make all the difference in getting your emails seen, opened, and clicked.
✅ Final Thought
Complaint rates are like cholesterol.
Silent. Deadly. But 100% manageable—if you’re paying attention.
Now that Gmail’s giving us campaign-level visibility, there’s no excuse to ignore it.
Just remember: Gmail’s only one part of the inbox battlefield.
You need a cross-ISP strategy if you want to scale safely and profitably.
Respect the inbox.
Watch your complaint rate.
Stay in control.
Chris Miquel
PS: If you’re not using Feedback-ID headers yet, now’s the time. Need help implementing it? Hit reply and I’ll walk you through it or point you in the right direction.
