If you’re running newsletters, doing outreach, or just trying to make sure people actually see your emails — you already know deliverability can be a pain. Messages land in spam. Fancy HTML gets mangled. Or worse, you’re not even sure what’s going wrong. If you’ve ever wanted a dead-simple way to test your emails and actually fix what’s broken, this guide is for you.
Let’s get straight to it: we’re going to walk through using Mail-tester to spot deliverability issues—and actually do something about them, without chasing your tail or getting lost in jargon.
Why Email Deliverability Still Sucks (And What You Can Actually Fix)
Most email “problems” fall into a few buckets:
- Your emails go to spam.
- They look broken (images missing, weird formatting).
- You get flagged as a spammer, even though you’re not.
A lot of advice out there is either too vague (“improve your sender reputation!”) or too technical (“check your DKIM alignment with OpenSSL!”). Mail-tester cuts through that by giving you a quick, real-world checkup of how your email stacks up.
This guide will show you how to use that info, not just stare at a score.
Step 1: Prep Your Real-World Test Email
Before you start fiddling with tools, send yourself the exact email you plan to send out—same subject line, content, links, headers, everything. This is important:
- Don’t use a “test” version with dummy text. Real spam filters look for real content.
- If you’re sending from Mailchimp, Outlook, or another platform, send it from there.
Pro Tip: Avoid sending test emails from a different account or using a different “from” address. Your real sender reputation matters.
Step 2: Get Your Unique Mail-tester Address
Head to Mail-tester. You’ll see a weird-looking email address, something like test-abc123@mail-tester.com.
- Copy that address.
- Don’t share it—each address is unique to your session.
Mail-tester is free for a few tests per day. If you’re running lots of campaigns, consider their paid option, but for most people, the free tier is enough.
Step 3: Send Your Real Email to Mail-tester
Paste the Mail-tester address into your email platform (as the recipient), then send your email exactly as you would to your real list.
- Make sure it goes through your actual sending infrastructure—not a different SMTP, not your personal Gmail.
- If you use automations or sequences, trigger it the real way.
What Not To Do: Don’t forward your email. That messes with headers and makes the test useless.
Step 4: Analyze Your Mail-tester Score
After a minute or two, refresh the Mail-tester page. You’ll get a score out of 10, plus a detailed breakdown. Here’s what to pay attention to—and what to ignore:
What Matters
- SpamAssassin Score: This mimics what actual spam filters do. If you’re getting flagged here, it’s a big deal.
- DNS Checks: SPF, DKIM, and DMARC are boring acronyms, but they matter. If these fail, your emails will get flagged.
- Blacklist Checks: If your sending IP or domain is blacklisted, you’ll see it. This is usually a red flag, especially if you’re on major lists like Spamhaus.
What’s Less Important
- Minor HTML warnings: If Mail-tester nitpicks tiny HTML issues (“no doctype!”), but your email displays fine, don’t sweat it.
- Reverse DNS pointers: Not every sending platform sets this up. Unless you’re self-hosting, you probably can’t fix it.
- Missing List-Unsubscribe header: This isn’t critical for everyone, but it’s useful for bulk senders.
Reality Check: A perfect 10/10 isn’t necessary. Many legit emails score 8–9 and do just fine.
Step 5: Fix the Issues That Actually Hurt Deliverability
Mail-tester points out a lot, but you don’t need to fix everything. Focus on what matters:
1. SPF, DKIM, and DMARC Failures
- SPF: This record says which servers can send email for your domain. Add or update it in your DNS settings. Most email services give you the exact value to paste.
- DKIM: This signs your emails to prove they're really from you. Again, your email provider gives you a record to add to DNS.
- DMARC: Adds a policy to handle failures. Not strictly required, but highly recommended.
Don’t Overthink: If you use a major provider (Mailchimp, Google Workspace, SendGrid), just follow their instructions. Don’t try to invent your own records unless you actually know DNS inside out.
2. Blacklist Warnings
- Check the list name. Some blacklists barely matter, others (like Spamhaus or Barracuda) are serious.
- If you’re hit, check the list’s removal process. Sometimes it’s automatic, sometimes you need to request removal.
- If you’re repeatedly blacklisted, something’s up—spam complaints, purchased lists, or a hacked account. Fix the root cause.
3. Spammy Content
- If Mail-tester flags “spammy words” or phrases, tweak your copy.
- Avoid too much ALL CAPS, excessive exclamation marks, or sketchy language (“earn $$$ fast!”).
- Don’t go overboard. Legitimate content can look spammy to scanners, but if it’s clear and honest, most filters won’t mind.
4. Broken HTML or Images
- Preview your email in real clients (Gmail, Outlook, Apple Mail).
- If images aren’t loading, check your URLs. Don’t use image hosting that blocks hotlinking.
- For HTML, stick to simple layouts. Fancy, complex HTML is more likely to break or get flagged.
5. Missing Unsubscribe Link
- For bulk or marketing emails, always include an unsubscribe link.
- Many inboxes (especially Gmail and Outlook) look for this and may automatically filter emails without it.
Step 6: Re-Test and Get a Baseline
Once you’ve fixed the key issues, send your email again to Mail-tester. See if your score improves, but—more importantly—see if the critical problems are gone.
Don’t chase perfection. Some issues (like minor HTML warnings) are harmless. Focus on not getting flagged for spam or authentication failures.
Step 7: Monitor Real-World Results
Mail-tester is a snapshot, not a guarantee. After sending to your real list:
- Keep an eye on open rates and bounce rates.
- If you see a big drop, or complaints, check again.
- Test every time you change something significant—new domain, new provider, or big content shifts.
Ignore the urge to obsess. If your emails are getting decent opens and aren’t bouncing to spam, you’re good.
Honest Truth: What Mail-tester Can’t (and Can) Do
What It Does Well:
- Flags setup mistakes (bad DNS, missing authentication).
- Gives a simple way to tweak content and see real spam filter reactions.
- Checks for blacklists that actually matter.
What It Doesn’t Do:
- Fix your sender reputation if you’ve already burned it.
- Tell you if Gmail, Outlook, or Yahoo will definitely put you in the inbox (they use secret sauce).
- Replace real testing with your actual audience.
Use Mail-tester as a tool, not gospel. It’s a great way to catch obvious problems, but no tool can guarantee inbox placement.
Keep It Simple, Test Often, Don’t Obsess
Email deliverability can make you want to pull your hair out, but it doesn’t have to be complicated. Use Mail-tester to catch the big stuff, fix what actually matters, and move on. Don’t get stuck chasing a perfect 10/10.
Test, fix, and send. That’s it. Iterate when you see problems—not just because some tool says so. And remember: most people never even check this stuff. You’re already ahead.