Deliverability

What is Email Deliverability?

Email deliverability is the measure of how successfully your emails reach recipients' inboxes rather than being blocked, bounced, or filtered to spam. It's determined by a complex interplay of factors including sender reputation, email authentication, content quality, and recipient engagement.

Deliverability vs Delivery Rate

These terms are often confused:

An email can be "delivered" (accepted by the server) but still end up in spam. True deliverability means reaching the inbox.

Factors Affecting Deliverability

1. Sender Reputation

Your sender reputation is a score that ISPs assign based on your sending behavior:

• IP reputation: History of the IP address sending your emails
• Domain reputation: History of your sending domain
• Sending patterns: Volume, consistency, and spikes
• Recipient engagement: Opens, clicks, replies, complaints

2. Email Authentication

Proper authentication proves you're authorized to send email for your domain:

• SPF: Specifies authorized sending IPs
• DKIM: Cryptographically signs your emails
• DMARC: Defines policy for authentication failures

3. Content Quality

Email content is analyzed for spam signals:

• Spam trigger words and phrases
• HTML to text ratio
• Image to text ratio
• Broken links
• Suspicious attachments
• URL reputation

4. List Quality

The health of your email list matters:

• Bounce rates
• Complaint rates
• Spam trap hits
• Engagement metrics
• List acquisition methods

5. Technical Infrastructure

Proper technical setup is essential:

• Valid reverse DNS (PTR records)
• Consistent sending IPs
• Proper email headers
• TLS encryption
• Correct MIME formatting

Measuring Deliverability

Key Metrics to Track

Tools for Measurement

// Get deliverability metrics from Transactional
const { data } = await client.analytics.getDeliverability({
  startDate: '2024-01-01',
  endDate: '2024-01-31',
});
 
console.log('Delivery rate:', data.deliveryRate);
console.log('Inbox placement:', data.inboxRate);
console.log('Spam placement:', data.spamRate);
console.log('Bounce rate:', data.bounceRate);
console.log('Complaint rate:', data.complaintRate);

Improving Deliverability

Authentication Checklist

1. Set up SPF: Add Transactional to your SPF record

   v=spf1 include:_spf.transactional.dev -all
   

2. Configure DKIM: Add the DKIM records we provide

   default._domainkey.example.com. IN TXT "v=DKIM1; k=rsa; p=..."
   

3. Implement DMARC: Start with monitoring, then enforce

   v=DMARC1; p=quarantine; rua=mailto:dmarc@example.com
   

List Hygiene

• Validate at signup: Use real-time email validation
• Use double opt-in: Confirm email ownership
• Remove bounces immediately: Never retry hard bounces
• Prune inactive subscribers: Remove after 6-12 months
• Never purchase lists: They contain traps and invalid addresses

Content Best Practices

• Balance text and images: Don't send image-only emails
• Include plain text version: Always send multipart emails
• Use reputable URLs: Avoid URL shorteners
• Personalize appropriately: Use recipient names when relevant
• Clear unsubscribe: Make it easy and honor immediately

Engagement Optimization

• Send relevant content: Segment your audience
• Optimize send times: Test when your audience engages
• Maintain consistency: Avoid sudden volume spikes
• Encourage interaction: Ask for replies and clicks

Common Deliverability Issues

Sudden Drop in Deliverability

Causes:

• IP or domain blocklisted
• Spike in complaints
• Changed sending patterns
• Infrastructure issues

Actions:

1. Check blocklist status
2. Review recent sends for issues
3. Verify DNS records are correct
4. Contact ESP support

Emails Going to Spam

Causes:

• Missing or failing authentication
• Content triggers
• Low engagement history
• Shared IP reputation issues

Actions:

1. Verify SPF, DKIM, DMARC pass
2. Run content through spam checkers
3. Improve engagement through better targeting
4. Consider dedicated IP

High Bounce Rates

Causes:

• Stale or purchased lists
• Typos in signup forms
• Lack of email validation

Actions:

1. Implement real-time validation
2. Use double opt-in
3. Regularly clean your list

Transactional vs Marketing Deliverability

Best Practice: Use separate sending domains for transactional and marketing email to protect your transactional deliverability.