Definition
Submission rate measures the percentage of emails successfully accepted by your sending infrastructure or ESP out of those submitted for delivery. A submission failure means your ESP rejected the email before attempting delivery to the mailbox provider. Common reasons include invalid authentication, formatting errors, attachment size limits, hourly or daily rate limits, and policy violations.
This metric is distinct from delivery rate and bounce rate. A high submission rate (99%+) indicates well-configured sending infrastructure. Low submission rates signal configuration problems that need attention before they affect broader deliverability.
Common Submission Failures
| Failure | Cause | Fix |
|---|---|---|
| Rate limit exceeded | Too many sends in a short period | Implement throttling or increase limits |
| Authentication failure | Missing or incorrect SPF/DKIM | Verify authentication records |
| Invalid recipient format | Malformed email addresses | Validate addresses before submission |
| Attachment too large | Over ESP size limits | Use hosted images and links instead |
| Suspicious content | Triggering ESP policy filters | Review against ESP content policies |
Best Practices
- Monitor submission rate alongside delivery rate for a complete picture
- Investigate any submission failure rate above 1%
- Implement pre-submission validation to catch formatting errors
- Use queuing and throttling to stay within rate limits
- Review changed authentication settings after DNS updates
- Coordinate with your ESP on rate limits during high-volume campaigns
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Frequently Asked Questions
A healthy submission rate is 99% or higher. Rates below 99% indicate configuration issues, rate limiting problems, or data quality issues that should be investigated and resolved promptly.
No. Submission rate measures acceptance by your sending infrastructure. Delivery rate measures acceptance by the recipient's mailbox provider after submission. A high submission rate with a low delivery rate indicates deliverability issues (e.g., poor sender reputation) rather than infrastructure problems.