Permanent failure rate tracks the percentage of your emails that couldn't be delivered to their intended recipients due to permanent issues. Unlike temporary delivery problems (like a full mailbox), permanent failures indicate that the email address is invalid, non-existent, or has permanently rejected your messages. This metric, combined with other engagement metrics, gives you a complete picture of your email performance.
Monitoring your permanent failure rate is crucial for:
- Maintaining a clean and engaged subscriber list
- Avoiding delivery issues that can affect your entire sending reputation
- Identifying potential problems with your subscriber acquisition methods
How it's calculated
Permanent failure rate is calculated by dividing the number of permanent failures (bounces and rejections) by the total number of emails sent:
For example, if you sent 1,000 emails and 20 permanently failed to deliver, your permanent failure rate would be 2%.
What's a good permanent failure rate?
Email industry standards suggest:
| Rating | Permanent Failure Rate |
|---|---|
| Excellent | Below 1% |
| Good | 1% - 2% |
| Concerning | 2% - 5% |
| Problematic | Above 5% |
If your permanent failure rate exceeds 2%, it's time to take action to clean your list and improve your subscription processes.
Reducing your permanent failure rate
According to Buttondown's domain monitoring standards, all newsletters should maintain a permanent failure rate of 1% or lower.
To lower your permanent failure rate:
- Use double opt-in: Require email confirmation during signup to verify addresses (this is mandatory per Buttondown's Acceptable Use Policy)
- Clean your list regularly: Remove email addresses that consistently generate permanent failures
- Improve your subscription forms: Add basic validation to prevent typos in email addresses
- Monitor trends: Watch for spikes in your permanent failure rate, which might indicate issues with new subscriber sources
- Regularly engage subscribers: Inactive subscribers are more likely to change email addresses or close accounts
A healthy list with a low permanent failure rate will help ensure your newsletters reach your audience consistently and protect your sending reputation in the long run. You should also monitor your complaint rate alongside this metric for comprehensive deliverability insights.