Mail Tester

Why test your email deliverability?

If your emails don't reach the inbox, you lose customers, sales, and trust. Without an email deliverability test, you're working blind.

An email tester (mail tester) analyzes your configuration by sending a real message from your production server. Unlike a simple DNS checker, it tests the complete email journey: authentication, routing, and standards compliance.

Common problems detected by email testing:

• Broken SPF → Your emails are blocked or marked as spam
• Invalid DKIM → Providers (Gmail, Outlook) don't trust your messages
• Missing DMARC → You're vulnerable to spoofing and phishing attacks
• Misconfigured DNS → MX, PTR or TXT records incomplete

How to use the email tester in 3 steps

Step 1: Generate a test address

Click "Start email test" above. The system generates a unique address like:

test-abc123@mail-test.captaindns.com

This address is valid for 10 minutes and is only used for your test.

Step 2: Send from your mail server

Use your production server (not Gmail if you're testing your business domain) to send an email to this address.

Important for reliable testing:

• Send from the domain you want to test
• Use your actual production mail server (Mailchimp, SendGrid, Exchange, etc.)
• Subject and body don't matter (you can just send "test")

Step 3: View your test results

Wait 10-30 seconds. You get:

• ✅ Trust score out of 100 (deliverability score)
• ✅ SPF, DKIM, DMARC status (pass/fail with technical details)
• ✅ DNS issues detected (MX, PTR, missing records)
• ✅ Recommended actions to fix each problem

What does the email tester analyze exactly?

SPF (Sender Policy Framework)

Checks if your sending server is authorized to send for your domain. This is the first line of defense against spoofing.

The test verifies:

• SPF record exists and syntax is valid
• Your server's IP is authorized in the list
• No DNS lookup limit exceeded (10 max)

Common problems detected:

• ❌ Missing SPF → Add a TXT record to DNS
• ❌ Too many DNS lookups (>10) → Reduce include directives
• ❌ Unauthorized IP → Add your IP or include to SPF record

DKIM (DomainKeys Identified Mail)

Checks the cryptographic signature proving the email wasn't modified in transit.

The test verifies:

• DKIM signature is present in headers
• Public key exists in DNS (DKIM selector)
• Signature is valid, not expired, and matches the key
• Key strength is adequate (2048 bits minimum recommended)

Common problems detected:

• ❌ No DKIM signature → Enable DKIM on your mail server or provider
• ❌ Missing public key → Publish the DKIM record in DNS
• ❌ Invalid signature → Incompatible keys or email modified by a relay

DMARC (Domain-based Message Authentication, Reporting & Conformance)

Checks if your domain has a policy to handle SPF/DKIM failures. DMARC protects against phishing by telling recipients what to do with unauthenticated emails.

The test verifies:

• DMARC record exists (_dmarc.yourdomain.com)
• A policy is defined (none/quarantine/reject)
• SPF and DKIM are aligned with the From domain
• Reporting addresses (rua/ruf) are configured

Common problems detected:

• ❌ Missing DMARC → Create the _dmarc.yourdomain.com record
• ❌ Too permissive policy → Change from p=none to p=quarantine or p=reject
• ❌ Alignment failed → Fix SPF or DKIM domain to match the From address

DNS configuration and infrastructure

The tester checks your overall email infrastructure configuration beyond authentication.

The test verifies:

• MX records correctly configured and accessible
• Reverse DNS (PTR) configured for sending IP
• Email headers compliant with standards (RFC 5322)
• No conflicting configuration between records

Real-world use cases

Case 1: Launching a new domain

Symptom: You're launching acme.com and want to send newsletters. You've never configured email authentication.

Action with the tester:

1. Configure SPF, DKIM, DMARC in your DNS
2. Run an email test from your server
3. Fix issues flagged before sending to customers

Result: Avoid blacklisting from the first mass send. Target score: 90+.

Case 2: Emails suddenly landing in spam

Symptom: Your emails all land in spam since yesterday. Customers aren't receiving invoices or order confirmations.

Action with the tester:

1. Test immediately with an email from your server
2. Check the score and detailed diagnostics
3. Identify the problem (often SPF or DKIM broken after a DNS change)

Result: Diagnosis in 30 seconds, delivery restored within hours.

Case 3: Email provider migration

Symptom: You're moving from Mailchimp to SendGrid (or any provider change). Need to verify everything works.

Action with the tester:

1. Before migration: test and note your current score
2. Configure new provider's SPF and DKIM in your DNS
3. Test from the new provider
4. Compare scores before/after

Result: No deliverability drop during migration. Immediate detection of configuration oversights.

Case 4: Regular production monitoring

Symptom: You send 100k emails/month. You want to maintain optimal deliverability and detect issues before they impact customers.

Action with the tester:

1. Schedule weekly or monthly tests
2. Monitor score trends
3. Fix issues as soon as they appear

Result: Stable delivery rate at 95%+. No surprises with customers who "didn't receive" your emails.

Deliverability score interpretation

Factors that impact the score:

• Valid and aligned SPF: +25 points
• Valid and aligned DKIM: +25 points
• DMARC configured with policy: +20 points
• Correct MX and PTR: +15 points
• Standards compliance: +15 points

FAQ - Frequently asked questions

Q: How does the email tester work?

A: Click "Start test", send an email to the generated address from your mail server, and we automatically analyze SPF, DKIM, DMARC, headers and DNS configuration. Results in 10-30 seconds.

Q: What does the deliverability score mean?

A: It's a score out of 100 that estimates your chances of reaching the inbox (inbox placement rate). It combines:

• Authentication: SPF, DKIM, DMARC pass or fail
• DNS configuration: MX, PTR, TXT records
• Compliance: RFC standards and best practices adherence

90+ = excellent, 70-89 = good, below 70 = issues to fix.

Q: How long does the analysis take?

A: 10-30 seconds after sending. The system waits for your email, analyzes authentication and displays results instantly. If nothing appears after 60 seconds, verify you sent to the correct address.

Q: Is the tester free?

A: Yes, 100% free with no signup. Generate a test address and send as many emails as you want. No usage limits.

Q: My score is low, what should I do?

A: The report shows exactly what's failing with fix instructions:

• SPF failed → Add your server to the SPF record
• DKIM missing → Enable DKIM at your email provider
• DMARC absent → Create a DMARC record
• DNS incorrect → Fix MX or PTR records

Q: Can I test multiple domains or servers?

A: Yes, start a new test for each domain or server you want to verify. Each test generates a unique, independent address. You can test:

• Different sending domains
• Different providers (Mailchimp, SendGrid, etc.)
• Production vs staging servers

Q: How often should I test my email configuration?

A:

• After every change: server migration, DNS modification, new provider
• Routine: monthly verification recommended in production
• When issues arise: as soon as customers report missing emails

Complementary tools

Useful resources

• DMARCbis: what's changing and how to prepare (CaptainDNS guide)
• DKIM2: what's new, removals and key dates (CaptainDNS guide)
• Google - Email sender guidelines (Gmail requirements for bulk senders)
• Microsoft - Email authentication in Microsoft 365 (Outlook/M365 guide)
• RFC 7208 - Sender Policy Framework (SPF) (official specification)
• RFC 6376 - DomainKeys Identified Mail (DKIM) (official specification)
• RFC 7489 - Domain-based Message Authentication (DMARC) (official specification)