Cold Emails Ended Up in CTO's Blacklists

Welcome to Issue #4 of RevGen Labs Report.

Last week, I received a panicked call from an agency owner who suddenly saw their open rates plummet from 45% to under 5%.

Their cold email campaign had hit the dreaded blacklist wall.

And it happens to the best of us.

What we're covering today:

• The 3 critical levels where blacklisting occurs (and most people only know about one)

• Why your perfectly "compliant" emails still get flagged

• The backup infrastructure you absolutely need before sending your first campaign

Before we dive in, quick reminder that I go live every Tuesday with agency founders to talk sales strategy.

This week, we've got automation experts Noel Maniraguha joining us. Noel will be sharing secrets to automate 90% of your business.

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The 3 Levels of Email Blacklisting Most People Miss

When your emails stop landing in inboxes, the problem is likely at one of these three levels:

1. Server Level Blacklisting

When your sending server gets flagged, everything stops working – regardless of which email address or domain you're using.

I've seen companies spend weeks troubleshooting their copy when the real problem was their server IP had been blacklisted by every major ISP.

Real example: An agency client was sending from an AWS EC2 instance that got flagged. Gmail, Yahoo, and Outlook rejected 100% of their emails – even after they changed domains and email addresses.

The fix: You'll need to replace the entire server and purchase new mailboxes if using private ESPs (this isn't possible with public ESPs like Gmail).

2. Domain Burnout

Your sending server looks clean, but your actual domain (yourcompany[dot]com) has been flagged.

Real example: A SaaS client couldn't figure out why their follow-ups were landing in spam. Turns out their domain had been reported enough times that it was automatically filtered – despite having perfect technical setup.

The fix: You need pre-aged alternate domains ready to deploy. We always keep 50+ warmed-up domains in our back pocket for serious outreach campaigns.

3. Mailbox Blacklisting

Sometimes it's just the specific email address that's the problem, not your entire domain.

Real example: A client's sales@company[dot]com address was blacklisted, but when they switched to mark@company[dot]com, deliverability instantly improved by 37%.

The fix: Purchase new diversified mailboxes while keeping your current domains. Rotate them strategically based on audience segments.

Your Infrastructure Seems Fine But You're Still Getting Blacklisted?

Here's why this happens to even careful senders:

1. Too Many Spam Reports

When recipients click that "Spam" button, it's like getting a strike against you. ISPs often use complaint thresholds as low as 0.1-0.3%.

That means for every 1,000 emails you send, just 1-3 spam reports can start the blacklisting process.

2. Outdated Contact Lists

Every bounced email signals to providers that your list isn't fresh.

Worse yet, "spamtrap" addresses hiding in purchased lists will trigger automatic blacklisting. I've seen entire campaigns derailed by a single honeypot address.

3. Sudden Jumps in Sending Volume

Real email lists grow gradually. Adding thousands of contacts overnight looks suspicious and triggers filtering algorithms.

One client ramped from 50 to 5,000 emails per day and immediately got flagged. We had to slowly rebuild their sending reputation over 6 weeks.

4. The Backup Infrastructure You Need Before Sending

After thousands of campaigns, here's what I consider essential:

• Multiple pre-aged domains (at least 3-6 months old)

• Diverse mailboxes across different providers

• Clean sending IPs with established sending history

• Proper technical setup (SPF, DKIM, DMARC)

• Gradual volume increases (never more than 30% per week)

📥 Want to land in every CTO and CEO’s primary inbox? 

We operate cold email systems that consistently reach inboxes daily at scale. Here’s the proof: 

👉Book a call with me.

Let's create a solution that truly delivers results.

Christian Oland
Co-founder RevGen Labs & RevReply