So you ran your latest campaign email through a spam checker and got a bunch of numbers and cryptic warnings. Now what? If you’re sending emails for business—newsletters, onboarding, sales, whatever—those spam scores aren’t just technical trivia. They’re the difference between landing in someone’s inbox or getting buried in spam.
This guide is for anyone who actually wants to understand what Mail-tester is telling them—and, more importantly, what to do about it. We’ll cut through the noise, flag the stuff that matters, and show you how to use these results to send better emails.
What is Mailtester, and why should you care?
Mail-tester is a free tool that tells you how likely your email is to end up in the spam folder. You send a real email to their randomly generated address, and it gives you a score out of 10, along with a breakdown of what’s helping or hurting your deliverability.
Why bother? Because even if you’re not spamming, spam filters are ruthless—and small technical mistakes (or just bad luck) can tank your reach. If your score is below 8/10, expect problems. But even a “perfect” 10/10 doesn’t guarantee you’ll avoid spam; it just means you’ve dodged the most obvious issues.
Step 1: Sending a Test Email to Mail-tester
Let’s start simple:
- Go to Mail-tester.
- Copy the unique email address they give you.
- Send your real campaign email to that address. Don’t just forward—send it as you would to your real list.
Pro tip: Use the actual sending system (Mailchimp, Gmail, whatever) you plan to use for your campaign. Don’t copy-paste into another email client, or you’ll get misleading results.
Wait a moment, then check your score. Now the real work begins.
Step 2: Reading the Overall Spam Score
Mail-tester will show you a number out of 10, usually with a green/yellow/red background. Here’s how to read that:
- 9 – 10: You’re in good shape. No major technical issues.
- 7 – 8.9: Fixable problems. You might still make the inbox, but you’re taking unnecessary risks.
- Below 7: Something’s seriously wrong. Expect to be flagged as spam.
Don’t obsess over a perfect 10, but if you’re in the red or yellow, take it seriously.
Step 3: Decoding the Breakdown—What Each Section Means
Mail-tester splits its results into a few main sections. Let’s walk through the ones that matter (and flag the ones you can mostly ignore).
1. SpamAssassin Score
This is the meat of the test. SpamAssassin is the same open-source engine a lot of mail providers use to filter spam. It’ll give you a number (usually negative is good, positive is bad), plus a list of “rules” that hit or missed.
Common flags and what to do:
- BODY: HTML_IMAGE_ONLY_XX: Your email is mostly images, not much text. Add more real text—otherwise, filters assume you’re hiding spammy content.
- MIME_HTML_ONLY: Only HTML, no plain-text version. Add a plain-text alternative.
- DKIM_SIGNED / SPF_PASS / DMARC_PASS: These are your authentication basics. If any of these fail, fix them first (see next section).
- LOTS_OF_MONEY, URG_BIZ: Using language like “buy now,” “limited time,” etc. won’t automatically get you spammed, but don’t overdo it.
Ignore: - Tiny deductions for “missing” things like “List-Unsubscribe” on small campaigns. Big platforms add this for you anyway. - Warnings about “missing” MX or PTR records for your sending domain—if your main website sends the email, you’re likely fine.
2. Authentication: SPF, DKIM, DMARC
If you see red or yellow here, stop and fix these before worrying about anything else.
- SPF (Sender Policy Framework): Tells receivers which servers can send mail for your domain.
- DKIM (DomainKeys Identified Mail): Adds a digital signature showing the message is legit.
- DMARC: Builds on the above, telling receivers what to do if SPF or DKIM fail.
How to fix:
Usually, you need to add or update DNS records. Your email provider will have instructions. Don’t guess—get it right.
If you skip this, nothing else you do will matter.
3. Blacklists
Mail-tester checks if your sending IP or domain is on popular blacklists. Here’s the honest truth:
- If your IP is blacklisted: If you’re on a shared service (Mailchimp, SendGrid, etc.), you probably can’t do much. If it keeps happening, switch providers.
- If your domain is blacklisted: This is bad. Clean up your list, stop any risky sending, and request delisting. Sometimes, just waiting it out works.
Ignore:
Obscure blacklists that don’t affect major inboxes. Focus on real-world impact.
4. Content Analysis
Mail-tester tries to flag spammy content—ALL CAPS, too many links, suspicious attachments, or weird formatting.
- What works: Short, clear text; avoid dozens of links or images; don’t use huge font sizes or colored text everywhere.
- What doesn’t: Trying to “trick” filters with hidden text or ultra-minimalist designs. Spam filters are smarter than that.
Pro tip: If you’re writing like a real human, you’re already ahead of 95% of spammers.
5. Broken or Missing Elements
You might see warnings for:
- Missing “List-Unsubscribe” header (not a big deal for small lists, but add it if you can).
- Broken images or links (fix these, or just remove them).
- “Message appears to be a test” (ignore; you’re literally testing).
Step 4: What to Actually Fix (and What to Ignore)
Here’s where most people waste time: chasing every single warning. Don’t.
Fix immediately:
- SPF, DKIM, or DMARC failures
- Obvious blacklisting of your domain
- Major SpamAssassin hits (scores above +3 for a single rule)
Worth tweaking:
- Add more real text if your email is mostly images
- Add a plain-text version if missing
- Clean up broken links or images
- Tone down “shouty” sales language if you’re getting dinged for it
Ignore (for now):
- Tiny SpamAssassin deductions (-0.1, -0.2, etc.)
- Cosmetic warnings about “test” emails
- Obscure blacklist hits that don’t affect major providers
Remember: Deliverability is more than passing a test. List quality, engagement, and sending reputation matter just as much—Mail-tester can’t see those.
Step 5: Rinse and Repeat
Don’t expect to fix everything on the first try. Tweak, send another test, and see what changes. If you’re stuck on a warning you don’t understand, Google the exact message, or check your email provider’s help docs. Sometimes, it’s out of your control (especially on shared IPs).
Pro tip: Don’t obsess. If you’re scoring 9/10 and your important stuff is green, send your email and move on. Your time is better spent writing better content or improving your list.
Real-World Gotchas and Honest Advice
- Mail-tester isn't the final judge. Some emails “pass” but still go to spam at Gmail or Outlook. Watch your real-world open rates.
- Don’t chase perfection. Getting a 10/10 doesn’t guarantee inbox placement; it just means you’ve checked the technical boxes.
- Avoid spammy tricks. Don’t use invisible text, misleading subject lines, or fake reply chains. They might work short-term, but they kill your reputation.
Keep It Simple and Keep Sending
At the end of the day, Mail-tester is just a tool. Use it to catch the obvious issues, but don’t let it distract you from what matters: sending emails people actually want.
Fix the big stuff, don’t sweat the small stuff, and iterate. The more you send (and observe real results), the better you’ll get. Ignore the hype—consistency and clarity beat clever tricks every time.