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Email Deliverability Testing & Spam Prevention

Testing Tools​

1. Mail Tester (Best Overall)​

  • URL: https://www.mail-tester.com
  • How to use:
    1. Get a unique test email address from the site
    2. Send your email to that address
    3. Get a score out of 10 with detailed breakdown
  • Checks: SPF, DKIM, DMARC, content analysis, blacklists, HTML quality

2. GlockApps (Professional)​

  • URL: https://glockapps.com
  • Features:
    • Inbox placement testing across Gmail, Outlook, Yahoo, etc.
    • Spam filter analysis
    • Authentication checks
  • Cost: Paid (free trial available)

3. MXToolbox (DNS & Blacklist Checks)​

4. Google Postmaster Tools (For Gmail Delivery)​

  • URL: https://postmaster.google.com
  • Setup: Add and verify your domain
  • Provides:
    • Domain reputation score
    • IP reputation
    • Spam rate
    • Feedback loops
    • Authentication status

5. Microsoft SNDS (For Outlook/Hotmail)​

Common Spam Triggers to Check​

Authentication Issues (Most Common)​

  • SPF: Is it configured and passing?
  • DKIM: Is it signing correctly?
  • DMARC: Is it set to p=quarantine or p=reject?
  • From/Return-Path alignment: Do they match?

Content Issues​

  • Subject line: Avoid spam words (FREE, URGENT, !!!, $$$)
  • HTML quality:
    • Text-to-image ratio (at least 40% text)
    • No broken HTML
    • No forms in email
    • Responsive design
  • URLs:
    • Use HTTPS
    • No URL shorteners (bit.ly, tinyurl)
    • No blacklisted domains
    • Proper link text (not "click here")
  • Images:
    • Not too many images
    • Include alt text
    • No single-image emails

Technical Issues​

  • Reverse DNS (PTR): Does your IP resolve to your domain?
  • IP reputation: Check on Spamhaus, Barracuda, etc.
  • Domain age: New domains are often flagged
  • Sending volume: Sudden spikes trigger filters
  • Bounce rate: High bounces = bad reputation
  • Complaint rate: Keep under 0.1%

Missing Headers​

  • List-Unsubscribe: Should be present for bulk mail
  • Message-ID: Properly formatted
  • Date header: Present and accurate
  • From/Reply-To: Properly formatted

Quick Diagnostic Steps​

Step 1: Test Email Authentication​

# Send a test email and check raw headers
# Look for:
# - SPF: PASS
# - DKIM: PASS
# - DMARC: PASS

Step 2: Check Blacklists​

# Check if your IP/domain is blacklisted
curl "https://mxtoolbox.com/api/v1/Lookup/blacklist/YOUR_IP_OR_DOMAIN"

Step 3: Analyze Email Headers​

When email lands in spam:

  1. View full headers (Show Original in Gmail, View Source in Outlook)
  2. Look for X-Spam-Status or X-Microsoft-Antispam headers
  3. Check authentication results (Authentication-Results header)

Step 4: Content Analysis​

Send test email to mail-tester.com and fix issues with score < 8/10:

  • Broken HTML
  • Suspicious links
  • Spam words
  • Missing plain text version

Postchi-Specific Checks​

Verify Your Domain DNS Records​

# Check SPF
dig TXT email.studioaccolade.com | grep spf

# Check DKIM (use your selector)
dig TXT postchi._domainkey.email.studioaccolade.com

# Check DMARC
dig TXT _dmarc.email.studioaccolade.com

Check Actual Email Headers​

After sending, forward the email to yourself and check:

  • Does SPF pass?
  • Does DKIM signature verify?
  • Does DMARC pass?
  • Is Return-Path set correctly (VERP for bounce tracking)?

Common Fixes​

1. Outlook/Microsoft Going to Junk​

Most Common Issues:

  • Missing or failed DMARC
  • High spam complaint rate in SNDS
  • Content triggers (too many links, suspicious words)
  • New IP without reputation

Fixes:

  1. Register with Microsoft SNDS
  2. Set up DMARC with p=quarantine
  3. Implement feedback loops
  4. Warm up your IP properly
  5. Ensure proper authentication alignment

2. Gmail/Google Going to Spam​

Most Common Issues:

  • Failed authentication
  • Low engagement (low open rates)
  • High bounce/complaint rates
  • Sudden volume increase

Fixes:

  1. Register with Google Postmaster Tools
  2. Monitor domain/IP reputation
  3. Ensure engagement (good content)
  4. Clean your lists (remove bounces)
  5. Gradual volume increase

3. iCloud/Apple Going to Junk​

Most Common Issues:

  • Very strict content filtering
  • Failed authentication
  • Lack of engagement history

Fixes:

  1. Pristine authentication (SPF+DKIM+DMARC all passing)
  2. Clean, simple HTML (Apple is very strict)
  3. Strong subject lines (avoid spam words)
  4. Encourage users to move to inbox/whitelist

Immediate Actions for Postchi​

  1. Test Current Emails:

    # Send test to mail-tester.com
    curl -X POST http://localhost:3000/v1/batches \
      -H "Authorization: Bearer $TOKEN" \
      -H "Idempotency-Key: test-$(date +%s)" \
      -H "Content-Type: application/json" \
      -d '{
        "templateId": "YOUR_TEMPLATE_ID",
        "recipients": [{"to": "test-YOUR_ID@mail-tester.com"}]
      }'

  2. Check DNS Records:

    • Verify SPF includes your sending IP
    • Verify DKIM selector matches what you're signing with
    • Add DMARC if missing

  3. Monitor:

    • Set up Google Postmaster Tools
    • Register with Microsoft SNDS
    • Check blacklists weekly

  4. Content Improvements:

    • Add plain text version to all emails
    • Improve text-to-image ratio
    • Use descriptive link text
    • Add List-Unsubscribe header (already implemented for MARKETING)

Resources​

Monitoring Dashboard (Future Enhancement)​

Consider adding to Postchi:

  • Real-time bounce tracking
  • Complaint rate monitoring
  • Domain reputation score
  • Authentication status per email
  • Deliverability alerts