Mail-Tester: How to Use and Interpret Scores

How to Run a Test

1. Go to mail-tester.com
2. Copy the unique email address displayed (changes each visit)
3. Send your test email to that address from your actual sending system — same ESP, same domain, same authentication
4. Click "Then check your score"
5. Review the detailed breakdown

The key is step 3: send from your real infrastructure. Sending from your Gmail account to test an email that goes through SendGrid gives you meaningless results.

Understanding the Score

Mail-Tester breaks your score into sections, each contributing points:

Message Content (SpamAssassin)

SpamAssassin analyzes your email content and assigns point deductions for spam-like patterns:

Score Impact	Severity	Example
-0.1 to -0.5	Minor	Missing List-Unsubscribe header
-0.5 to -1.0	Moderate	High image-to-text ratio
-1.0 to -2.0	Significant	Known spam phrases, all-caps subject
-2.0+	Critical	Obfuscated URLs, hidden text

Each triggered rule is listed with its score impact. Address the highest-scoring rules first.

Authentication

Check	Points	What It Means
SPF pass	+1	Sending IP is authorized
DKIM pass	+1	Message signature is valid
DMARC pass	+0.5	Authentication aligns with policy
Missing SPF	-2	No SPF record or lookup failure
Missing DKIM	-1	No DKIM signature found

Authentication issues are the fastest points to recover. See our authentication guide.

Blacklists

Mail-Tester checks your sending IP against major blacklists. Each listing deducts points.

• Listed on 1-2 minor lists: -0.5 to -1.0
• Listed on Spamhaus or major list: -2.0 to -3.0
• Clean: No deduction

If you're listed, check our blacklist guides for delisting instructions.

HTML Quality

Minor deductions for:

• Missing alt text on images
• Non-standard HTML formatting
• Missing plain-text version of the message
• Broken HTML tags

Practitioner note: The most common score killers I see aren't content issues — they're authentication gaps. A missing DKIM signature costs you 1-2 points immediately. An SPF failure costs another 2. Fix authentication and most people jump from 6 to 9 overnight.

Score Interpretation Guide

Score	Assessment	Action
10/10	Perfect	Maintain current setup
9/10	Excellent	Minor tweaks optional
7-8/10	Good but improvable	Fix authentication gaps or content issues
5-6/10	Problems	Authentication likely failing; check blacklists
Below 5/10	Critical	Major infrastructure issues; stop sending until fixed

What Mail-Tester Can't Tell You

Mail-Tester is a content and authentication checker. It has significant blind spots:

No reputation data: Your domain or IP reputation — the single biggest deliverability factor — isn't measured. A brand-new domain scores 10/10 on Mail-Tester but may land in spam everywhere because it has no reputation history.

No engagement data: Gmail's #1 filtering signal is how recipients interact with your email. Mail-Tester can't measure this.

No real placement data: Mail-Tester doesn't tell you where Gmail, Outlook, or Yahoo would actually place your email. Use GlockApps or inbox placement testing for that.

Practitioner note: I've had clients show me a 10/10 Mail-Tester score and ask why they're in spam. Mail-Tester can't see that their domain reputation in Google Postmaster Tools is "Low" due to months of spam complaints. Use Mail-Tester for content/auth checks, Postmaster Tools for reputation, and GlockApps for actual placement.

Improving Your Score

Authentication fixes (biggest impact):

• Add or fix SPF record
• Enable DKIM signing
• Publish a DMARC record

Content fixes:

• Add a plain-text version of your HTML email
• Reduce image-to-text ratio
• Remove URL shorteners
• Add alt text to all images
• Include List-Unsubscribe header

Blacklist fixes:

• Check and delist from any active blacklists
• Address the root cause (list hygiene, compromised account, etc.)

Practitioner note: Run Mail-Tester on every email template you use, not just one test. I've found authentication passing on marketing email but failing on transactional email because they were sent through different systems with different DKIM configurations.

If your Mail-Tester score is low and you're not sure how to fix it, schedule a deliverability audit — I'll diagnose every deduction and fix the underlying issues.

Sources

• Mail-Tester: How It Works
• SpamAssassin: Rule Tests
• RFC 7489: DMARC
• RFC 6376: DKIM

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v1.0 · April 2026