Email Deliverability 101: Complete Beginner's Guide
Learn the fundamentals of email deliverability, sender reputation, and how to ensure your emails reach the inbox.
Email deliverability is the ability to successfully deliver emails to recipients' inboxes. While it sounds simple, modern email systems employ sophisticated filtering to protect users from spam, making deliverability a critical challenge for legitimate senders.
What is Email Deliverability?
Deliverability is not the same as delivery. An email can be technically delivered to a mail server but still never reach the inbox if it's filtered to spam or rejected entirely. True deliverability measures how many of your emails reach the intended inbox.
Key Metric
Industry average inbox placement rate is around 85%. Top performers achieve 95%+ by maintaining excellent sender reputation and list hygiene.
Understanding Sender Reputation
Your sender reputation is like a credit score for email. Internet Service Providers (ISPs) use this score to decide whether your emails deserve the inbox or should be filtered as spam.
Factors That Affect Sender Reputation
Bounce Rates
High bounce rates (>5%) signal poor list hygiene and damage reputation quickly. Keep bounces below 2% for healthy deliverability.
Spam Complaints
When recipients mark your email as spam, ISPs take notice. Complaint rates above 0.1% are concerning; above 0.3% can lead to blocking.
Engagement Metrics
Opens, clicks, replies, and forwards signal to ISPs that recipients want your emails. Low engagement indicates potential spam.
Sending Patterns
Sudden spikes in sending volume or erratic sending schedules appear suspicious. Maintain consistent sending patterns.
Authentication
Proper SPF, DKIM, and DMARC configuration proves you're authorized to send from your domain and protects against spoofing.
Email Authentication Essentials
Starting in 2024, Google and Microsoft require proper authentication for bulk senders. These protocols are now mandatory, not optional.
SPF (Sender Policy Framework)
SPF is a DNS record that lists which IP addresses are authorized to send email from your domain. When an email arrives, receiving servers check if it came from an authorized IP.
DKIM (DomainKeys Identified Mail)
DKIM adds a digital signature to your emails using cryptographic authentication. This proves the email hasn't been altered in transit and confirms it came from your domain.
DMARC (Domain-based Message Authentication)
DMARC builds on SPF and DKIM, telling receiving servers what to do if an email fails authentication checks. It also provides reporting so you can monitor your email authentication.
Bounce Management
Email bounces occur when messages can't be delivered. Understanding bounce types is critical for maintaining deliverability.
Hard Bounces
Permanent delivery failures caused by invalid email addresses, non-existent domains, or blocked addresses. Remove hard bounces immediately and permanently from your list.
Soft Bounces
Temporary issues like full mailboxes, server problems, or message size limits. Retry soft bounces a few times, but if they persist, treat them as hard bounces.
Block Bounces
Emails rejected by the receiving server due to content, sender reputation, or blocklist presence. These require immediate investigation and remediation.
List Hygiene Best Practices
Maintaining a clean email list is the foundation of good deliverability. Here's how to keep your list healthy:
- 1. Use Double Opt-In: Require new subscribers to confirm their email address. This eliminates typos and fake signups.
- 2. Validate at Signup: Implement real-time email validation on your signup forms to catch invalid addresses immediately.
- 3. Clean Regularly: Run bulk validation on your entire list quarterly to remove addresses that have become invalid.
- 4. Remove Inactive Subscribers: If someone hasn't engaged in 6-12 months, either re-engage or remove them.
- 5. Honor Unsubscribes Immediately: Process unsubscribe requests within 24 hours (ideally instantly) to avoid spam complaints.
- 6. Never Buy Lists: Purchased lists contain invalid addresses, spam traps, and people who didn't opt in—all reputation killers.
Content and Formatting
Even with perfect authentication and list hygiene, poor content can trigger spam filters.
Avoid Spam Triggers
- Excessive use of ALL CAPS or excessive punctuation!!!
- Spam trigger words like "FREE", "ACT NOW", "GUARANTEED"
- Heavy image-to-text ratio (include sufficient text)
- Misleading subject lines that don't match content
- Excessive links or hidden links
Best Practices
- Use a recognizable sender name and address
- Write clear, honest subject lines
- Include plain text version alongside HTML
- Provide clear unsubscribe link (required by law)
- Include physical mailing address (CAN-SPAM requirement)
Monitoring Your Deliverability
Track these metrics to maintain healthy deliverability:
Critical Metrics
- • Bounce rate (keep below 2%)
- • Spam complaint rate (keep below 0.1%)
- • Inbox placement rate
- • Blocklist status
Engagement Metrics
- • Open rate
- • Click-through rate
- • Unsubscribe rate
- • Reply rate
Taking Action
Good deliverability doesn't happen by accident. It requires ongoing attention to authentication, list hygiene, content quality, and engagement. Start with these foundational steps:
Set up SPF, DKIM, and DMARC for your sending domain
Implement email validation on all signup forms
Clean your existing list with bulk validation
Set up monitoring for bounce rates and spam complaints
Establish regular list cleaning schedule (quarterly minimum)