How to troubleshoot blacklisting issues using Mailtester insights

If your emails are hitting spam or just not arriving, you’re probably already annoyed—and for good reason. Maybe you ran your latest newsletter through a deliverability tool and saw the dreaded “blacklisted” warning. Now what? This guide is for folks who actually send email and want real answers, not hand-waving. We’ll walk through using Mail-tester to dig into blacklisting issues, what its results really mean, and how to take concrete steps to solve the problem.

Why you should care about blacklisting

Blacklists aren’t just for spammers—sometimes, legitimate senders get snagged, too. All it takes is one bad link, a misconfigured server, or sharing an IP with a bad neighbor. The result? Your emails go nowhere, your customers don’t see your messages, and your sender reputation tanks.

The good news: Most blacklist issues can be fixed, but only if you know exactly what’s going on. That’s where Mail-tester comes in.

Step 1: Run a test with Mail-tester

Start by sending a real copy of your actual marketing or transactional email to the unique address provided by Mail-tester. Take the email straight from your email platform—not a “test” button, but an actual send, so you get the real headers and content.

  • Go to Mail-tester.
  • Copy the email address it gives you.
  • Send your message from your real sender address.

Pro Tip: If you’re testing for a client, make sure they send it themselves. The sending infrastructure matters a lot.

After a few seconds, you’ll get a report with a score and a bunch of technical details. Ignore the score for now—we care about the blacklist section.

Step 2: Read (not just scan) the blacklist section

Mail-tester checks your sending IP against a bunch of major DNS-based blacklists (DNSBLs). These are public lists that mail servers consult to decide whether to accept your mail.

What you’ll see:

  • A list of blacklists, each showing whether your IP is “listed” or “not listed.”
  • Sometimes a note about which blacklist(s) you’re on.

What matters: - If you’re “listed” on any major blacklist (Spamhaus, Barracuda, SORBS, etc.), that’s a problem. - Ignore obscure blacklists you’ve never heard of. Some are basically useless or only used by a handful of small ISPs. - If you’re listed on Spamhaus, take it seriously. Most big providers check it.

What doesn’t matter: - Being listed on a tiny, regional blacklist nobody uses. - Minor warnings about “possible” issues if your real-world delivery is fine.

Step 3: Double-check with the blacklist directly

Mail-tester is a handy snapshot, but sometimes results lag or are cached.

  • Look up your sending IP in the major blacklists directly (e.g., Spamhaus, Barracuda, SORBS).
  • Go to their official lookup tools—just Google “Spamhaus lookup” and paste in your IP.
  • Check if you’re actually listed and what the reason is.

Why bother? Sometimes Mail-tester reports a listing that’s already been cleared, or vice versa.

Heads up: If you’re on multiple reputable blacklists, you have a bigger issue—skip ahead to Step 6.

Step 4: Diagnose why you’re listed

Most blacklist lookup tools will tell you why you’re on the list. Typical reasons:

  • Spam reports or complaints
  • Sending from a residential (not business) IP
  • Open relay or compromised server
  • Previous user of your shared IP was a spammer

What actually helps: - Read the description carefully. Don’t waste time fixing stuff that’s not the actual problem. - If you’re on shared hosting or a mass email platform, your neighbors’ bad practices might be to blame.

What doesn’t help: - Obsessing over minor “reputation” warnings. - Fixating on your content if the blacklist says it’s a technical or server issue.

Step 5: Fix the root cause

Here’s where most guides get vague. Let’s be concrete:

  • Spam complaints: Clean your list. Stop emailing people who never open. Make unsubscribing dead simple.
  • Compromised server/open relay: Lock down your mail server. Patch everything. Disable relaying.
  • Bad neighbor on shared IP: Contact your provider and ask for a new IP, or consider moving to a reputable sending service.
  • Technical misconfigurations: Check your SPF, DKIM, and DMARC records. Misconfigured authentication is a fast path to blacklists.

Pro Tip: Use the rest of the Mail-tester report to spot authentication or header issues. But don’t chase every warning—prioritize what matters for major blacklists.

Step 6: Request delisting—carefully

Once you’ve fixed the problem, request removal from the blacklist. Don’t bother if you haven’t addressed the root cause—they’ll just relist you.

  • Each blacklist has its own process. For Spamhaus, fill out their form and explain what you fixed.
  • Be honest, brief, and specific. No need for a sob story.
  • Some blacklists delist automatically after a period of clean sending; others require manual requests.

What to ignore: - Services that promise instant delisting for a fee. Most are scams or pointless. - Overly broad “reputation repair” outfits.

Step 7: Monitor and repeat—don’t assume you’re done

Blacklist issues can come back if you don’t change your habits.

  • Keep checking with Mail-tester every few weeks, or before a big send.
  • Use inbox placement tools if you’re sending lots of mail.
  • Watch bouncebacks for clues—sometimes a provider will quietly block you without saying “blacklist.”

Pro Tip: Set up alerts for your sending IP or domain at major blacklist monitoring services. Most are free or cheap.

What works, what’s hype, and what to ignore

Let’s cut through the noise:

  • What works: Actually fixing the real reason for blacklisting, not just tweaking your subject line or content. Consistent, authenticated sending from clean lists.
  • What’s hype: Expensive “deliverability optimization” services that don’t actually fix root causes. SEO-style “blacklist repair” pitches.
  • What to ignore: Obscure blacklists, minor warnings, or Mail-tester’s score if your delivery is actually fine.

Keep it simple—then iterate

Solving blacklisting isn’t magic. It’s mostly about understanding what’s really going wrong, making concrete fixes, and monitoring over time. Use Mail-tester as a tool, not a crystal ball. Focus on the big blacklists, fix what matters, and don’t get sidetracked by every yellow exclamation mark. Check regularly, keep your list clean, and you’ll spend less time fighting the spam folder and more time actually reaching your audience.