Email Deliverability Overview
Understanding email deliverability metrics and how OptiMail helps you improve inbox placement.
Last updated: 2026-01-27
Email Deliverability Overview
Email deliverability determines whether your emails reach the inbox or get filtered to spam. This guide explains key deliverability concepts and how OptiMail helps you maintain a healthy sender reputation.
What is Email Deliverability?
Email deliverability is the ability to successfully deliver emails to recipients' inboxes. It's different from email delivery:
- Email Delivery - Your email reached the recipient's mail server (not bounced)
- Email Deliverability - Your email landed in the inbox (not spam folder)
An email can be "delivered" but still end up in spam. Deliverability is what matters for engagement.
Key Deliverability Metrics
Inbox Placement Rate
The percentage of emails that reach the primary inbox vs. spam folder.
- Excellent: >95%
- Good: 85-95%
- Needs Improvement: 70-85%
- Poor: <70%
Bounce Rate
The percentage of emails that couldn't be delivered.
Hard Bounces - Permanent failures:
- Invalid email addresses
- Non-existent domains
- Blocked addresses
Soft Bounces - Temporary failures:
- Full mailbox
- Server temporarily unavailable
- Message too large
Target: Keep bounce rate under 2%
Spam Complaint Rate
The percentage of recipients who mark your email as spam.
- Acceptable: <0.1% (1 per 1,000 emails)
- Warning: 0.1-0.3%
- Critical: >0.3%
Note: Even a small spam complaint rate can significantly impact deliverability.
Engagement Metrics
Mailbox providers track recipient engagement to determine inbox placement:
- Open Rate - Percentage who opened your email
- Click Rate - Percentage who clicked a link
- Reply Rate - Percentage who replied
- Delete Without Opening - Negative signal
Higher engagement = better inbox placement.
Email Authentication
Proper authentication proves you're authorized to send from your domain. OptiMail monitors three key protocols:
SPF (Sender Policy Framework)
SPF specifies which servers can send email for your domain.
Status meanings:
- Pass - Email sent from authorized server
- Fail - Server not authorized (likely spam)
- None - No SPF record found
DKIM (DomainKeys Identified Mail)
DKIM adds a digital signature to verify email wasn't altered.
Status meanings:
- Pass - Signature valid
- Fail - Signature invalid or missing
- None - No DKIM configured
DMARC (Domain-based Message Authentication)
DMARC tells receivers how to handle emails that fail SPF/DKIM.
Policies:
- None - Monitor only, don't reject
- Quarantine - Send failures to spam
- Reject - Block failures entirely
Recommendation: Start with "none", move to "quarantine", then "reject" as you verify authentication.
Domain & IP Reputation
Your sending reputation determines how mailbox providers treat your emails.
Domain Reputation
Based on:
- Historical sending behavior
- Engagement rates
- Spam complaints
- Authentication status
IP Reputation
Based on:
- Volume of email sent
- Bounce rates from that IP
- Spam trap hits
- Blacklist status
OptiMail monitors your IP addresses against major blacklists and alerts you to any issues.
The OptiMail Deliverability Score
OptiMail calculates a comprehensive deliverability score (0-100) based on:
| Factor | Weight | Description |
|---|---|---|
| Inbox Placement | 30% | Where emails are landing |
| Bounce Rate | 20% | Hard and soft bounces |
| Authentication | 20% | SPF, DKIM, DMARC status |
| Engagement | 15% | Opens, clicks, replies |
| Reputation | 15% | Domain/IP standing |
Score Ranges
- 90-100: Excellent - Your emails consistently reach inboxes
- 80-89: Good - Minor issues to address
- 70-79: Fair - Noticeable deliverability problems
- 60-69: Poor - Significant issues affecting inbox placement
- Below 60: Critical - Immediate action required
Common Deliverability Issues
Sudden Drop in Delivery
Possible causes:
- Hit a spam trap
- Large spike in complaints
- Sending volume increased too quickly
- Authentication misconfigured
Gradual Decline
Possible causes:
- List aging (addresses becoming invalid)
- Declining engagement
- Content triggering spam filters
- Competitor complaints
New Domain/IP Issues
New sending infrastructure has no reputation:
- Start with low volumes
- Gradually increase (warming)
- Focus on engaged recipients first
Improving Your Deliverability
List Hygiene
- Remove bounces immediately - Never resend to hard bounces
- Sunset unengaged subscribers - After 6-12 months of no engagement
- Use double opt-in - Confirms valid, interested subscribers
- Monitor spam traps - Indicates list quality issues
Content Best Practices
- Maintain text/image ratio - Don't send image-only emails
- Avoid spam trigger words - "Free", "Act now", "Limited time"
- Include unsubscribe link - Required by law, improves trust
- Use consistent From name - Recipients should recognize you
Sending Practices
- Warm up new IPs/domains - Gradually increase volume
- Send consistently - Avoid sporadic, high-volume blasts
- Segment by engagement - Prioritize active subscribers
- Test before sending - Use inbox placement testing
OptiMail Alerts & Recommendations
OptiMail automatically monitors for issues and provides:
Real-Time Alerts
- Bounce rate spikes
- Spam complaint increases
- Authentication failures
- Blacklist additions
- Engagement drops
AI-Powered Recommendations
Based on your data, OptiMail suggests:
- Best times to send
- Content improvements
- List segments to focus on
- Technical fixes needed