🎙️The Day I Watched a Publisher Lose 34% of His List Overnight (And Didn't Know Why)

A few months ago, I got a panicked call from a publisher friend.

"Chris, something's wrong. Our email just... stopped working."

He'd been sending consistently for 18 months. Strong engagement. Solid open rates. Then overnight—literally overnight—his numbers cratered.

Open rates dropped from 45% to 11% in a single day.

His first instinct? Blame the content. Maybe the subject line was off. Maybe people were tired of his format. He started questioning everything—his value prop, his audience fit, whether he should pivot his entire editorial strategy.

I asked him one question: "Did you check Spamhaus?"

Silence.

"What's Spamhaus?"

That's when I realized: Most newsletter operators have no idea this infrastructure layer even exists.

They think deliverability is about subject lines and send times. They don't realize there's an entire technical foundation sitting underneath their ESP that can silently destroy their reach overnight.

Turns out, his sending IP had gotten blocklisted—probably from a list bombing attack he didn't even know happened—and 80% of his emails were getting rejected at the server level before anyone even had a chance to open them.

He wasn't having a content problem. He was having an infrastructure problem.

And he had no idea where to even start looking.

After that call, I knew I needed to get another deliverability expert on Audience Bridge Insights to break down what's actually happening under the hood of email deliverability.

Not the surface-level stuff everyone talks about—subject lines, send times, engagement tactics—but the technical infrastructure issues that silently kill inbox placement and most newsletter operators don't even know exist.

LB Blair is what I'd call an "email mechanic"—a full-stack email solutions architect who's worked with everyone from top newsletters to massive e-commerce brands, fixing problems most senders don't realize are breaking their deliverability.

Her background is in computer forensics and IT audit, which means she approaches email deliverability like a detective. When something breaks, she knows exactly where to look—blocklists, authentication protocols, content construction, IP reputation, ESP infrastructure.

She's helped audit companies like Milk Road before their sale, saved clients millions in infrastructure costs, and regularly fixes deliverability issues that other "experts" couldn't diagnose.

When I sat down with her, I wanted answers to the questions newsletter operators actually have but don't know how to ask:

What I got was a masterclass in forensic email troubleshooting.

Here's what we uncovered (and some of this is gonna sting):

LB told me something I didn't expect: Content filtering is back, but it's not about "spam words" anymore.

Google and Microsoft are filtering based on technical construction—bloated HTML from drag-and-drop editors, oversized images pulled straight from your CMS, and non-secure tracking links.

"Don't just grab a 2MB hero image off your website and drop it in your email," she said. "If that image takes more than half a second to load on mobile, you've already lost them."

Her fix: Use TinyPNG.com for lossless compression before uploading anything to your ESP. It can cut file sizes by up to 80% without losing quality.

One of her clients was unknowingly sending 4MB images in every campaign. After compression, their inbox placement jumped 23% in two weeks.

Cost to implement: $0. Time required: 2 minutes per image.

Here's a nightmare scenario LB walked me through:

Hackers find your open web form. They flood it with fake or stolen email addresses tied to financial accounts they're trying to compromise. Your autoresponder fires off welcome emails to all of them. Half bounce. Half complain. Your sender reputation craters.

"If you start getting a bunch of welcome emails you didn't sign up for, that's a sure sign someone's about to hit your financial accounts," she said.

I explained my strategy:

As she put it: "You need defense in depth. Belt, suspenders, and a backup plan."

She also called me a cyber security expert.

When Gmail and Yahoo announced sender requirements back in 2023, most people set up SPF and DKIM but half-assed their DMARC policy.

LB's advice: Start with p=none for 45 days to collect reports. Then move straight to reject once everything's authenticating properly.

Skip quarantine unless you're actively under attack.

She told me about a client whose IT team deployed DMARC at p=reject without testing first. Their HubSpot emails all bounced. Then two weeks later, their NetSuite billing emails bounced—and half their customers didn't pay their invoices that month because they never received them.

"This is why you test at p=none first," she said. "So you catch the stuff you didn't know was sending from your domain."

Once you're clean? DMARC at reject makes you an unattractive target for spoofers. And unlocks BIMI, which can add a 10-15% open rate lift.

LB broke this down simply and I completely agree:

Stay on shared IPs if:

Go dedicated once:

"Spam filters are risk management systems that hate variance," she said. "If you spike way above your 30-day average, you're triggering anomaly detection every time."

One client was on shared IPs sending 500K/month. They moved to dedicated, warmed properly, and saw their Gmail inbox placement jump from 62% to 91% in six weeks.

I asked her the question I wish I'd known to ask my publisher friend: "If a sender's open rate falls off a cliff overnight, what's the first thing you look at?"

Her diagnostic checklist:

"If it cratered overnight, something changed fast," she said. "It's usually an event—a blocklisting, a bad link, or someone reported malware on your site."

She also just dropped a new tool from Spamhaus that lets you check your domain reputation across multiple dimensions.

Google officially started enforcing this in Q4 2024.

LB's already seen senders punished for broken unsubscribe implementations—even when their ESP was the one mishandling the header.

"If your unsubscribe process isn't instant and universal across all lists, fix it now," she said.

She found a client on Go High Level where the one-click unsubscribe wasn't actually unsubscribing people due to a broken HTTP post process. They were flagged in Postmaster Tools and their reputation tanked.

The fix took 20 minutes. The damage took two months to recover from.

LB's helped clients save millions by auditing their sending infrastructure.

Her recommendations:

"If you're getting 50% open rates and boosting platform reputation, tell them," she said. "You're the sender they want on their system."

Before selling a newsletter or media business, LB recommends auditing:

"Email isn't just part of financial due diligence anymore," she said. "Email is due diligence."

She helped audit Milk Road before their sale to make sure there were no hidden deliverability landmines that would crater valuations.

Most newsletter operators think deliverability is about subject lines and send times.

It's not.

It's about infrastructure. Authentication. Image compression. Bot protection. IP reputation. Contract optimization.

Because when your deliverability craters, you don't have time to Google solutions. You need someone who's seen the problem 50 times before and knows exactly where to look.

I'm opening up 5 Free Deliverability Audit calls this week.

We'll look at your current sending infrastructure, check for hidden issues that could be killing your inbox placement, and show you exactly what needs to be fixed before it costs you real money.

Click here for your private booking link.

(If you're sending 100K+ emails per month and haven't checked your Spamhaus reputation, blocklisting status, or DMARC policy in the last 30 days, you need this call.)

It’s all about your foundation,

Chris Miquel

PS: Remember that publisher friend whose deliverability tanked overnight? He's back to 43% open rates now. Took three weeks to fully recover. Could've been three hours if he'd known what to check first.

BEFORE YOU GO

This is just the surface. The full conversation with LB Blair is packed with forensic troubleshooting tactics most ESPs will never tell you about.

🎧 Listen now 👈