Definition
Email quality score is a calculated rating that reflects the overall health and quality of an email sender's practices. While the exact formula varies by ISP, quality scores typically consider subscriber engagement (opens, clicks), complaints, bounces, spam trap hits, authentication setup, and sending consistency.
A high quality score means ISPs will route your emails to the inbox. A low quality score means your emails are more likely to be filtered to spam or blocked entirely.
Factors Influencing Quality Score
| Factor | Weight (Approximate) | Description |
|---|---|---|
| Engagement rate | 30-40% | How many recipients open and click |
| Complaint rate | 20-30% | How many recipients mark as spam |
| Bounce rate | 10-15% | Percentage of invalid addresses |
| Spam traps | 10-15% | Hits on known trap addresses |
| Authentication | 5-10% | SPF, DKIM, DMARC configuration |
| Sending consistency | 5-10% | Volume patterns and frequency |
| Content quality | 5% | Spam score, text-to-image ratio |
How ISPs Use Quality Scores
| Score Range | Classification | Treatment |
|---|---|---|
| 90-100 | Excellent | Full inbox delivery |
| 70-89 | Good | Normal delivery, occasional filtering |
| 50-69 | Fair | Increased filtering, partial spam placement |
| 30-49 | Poor | Significant spam placement, throttled sending |
| 0-29 | Critical | Near-total spam placement, likely blocked |
Improving Your Quality Score
- Maintain complaint rates below 0.1% (use feedback loops)
- Remove hard bounces immediately
- Implement a sunset policy for inactive subscribers
- Authenticate all sending domains (SPF, DKIM, DMARC)
- Maintain consistent sending patterns (volume, frequency)
- Use double opt-in to ensure list quality
- Monitor and respond to spam trap hits
- Keep spam score below 5 (use content pre-scanning tools)
Quality Score Monitoring
- Sender Score (Validity): Industry-standard reputation score (0-100)
- Google Postmaster Tools: For Gmail-specific quality metrics
- Microsoft SNDS: For Outlook/Hotmail-specific data
- ESP reputation monitoring: Most ESPs provide reputation dashboards
- 250ok / Validity: Third-party reputation monitoring platforms
Related Glossary Terms
AOL Mail for Email Marketers
AOL Mail is a legacy email provider with specific deliverability requirements and rendering quirks, now operating as part of the Yahoo+AOL network under shared infrastructure.
BIMI
BIMI (Brand Indicators for Message Identification) is an email standard that allows brands to display their logo next to their emails in supported email clients. It requires DMARC enforcement at quarantine or reject policy.
Bounce Rate
Email bounce rate is the percentage of emails that were rejected by the receiving server before reaching the recipient. It is a key indicator of list health and data quality.
Email Deliverability
Email deliverability is the ability to land in the recipient's inbox rather than the spam folder. It depends on sender reputation, authentication, list quality, and content practices.
DKIM (DomainKeys Identified Mail)
DKIM (DomainKeys Identified Mail) is an email authentication method that uses digital signatures to verify that an email was not tampered with during transit and comes from a authorised domain.
DMARC (Domain-based Message Authentication)
DMARC (Domain-based Message Authentication, Reporting and Conformance) is an email authentication protocol that builds on SPF and DKIM to prevent domain spoofing and provide reporting on authentication failures.
Frequently Asked Questions
A Sender Score above 80 is considered good. Above 90 is excellent. Below 70 indicates significant deliverability risk. Sender Score aggregates data from major ISPs and is one of the most widely used quality indicators in the email industry.
Quality scores can change rapidly — a single bad campaign with high complaints can drop your score within hours. Recovery is slower, typically taking 2-4 weeks of consistent good practices to rebuild a damaged score.
Yes. Each ISP calculates its own quality score based on its specific data. You may have an excellent score with Gmail but a poor score with Outlook. Monitor per-ISP metrics using Google Postmaster Tools and Microsoft SNDS for the most accurate picture.