hen an email cannot be delivered, it “bounces” back to our servers. Understanding the difference between a temporary hiccup and a permanent dead-end is vital for keeping your sender reputation healthy and your Sendonyx account in good standing.
1. What is a Hard Bounce?
A Hard Bounce is a permanent delivery failure. This means the email address is invalid or no longer exists. There is zero chance that this email will ever be delivered.
- Common Causes: Typo in the email address (e.g.,
@gmaill.com), the recipient deleted their account, or the domain name doesn’t exist. - The Action: Sendonyx automatically blacklists hard bounces for you. You should never attempt to send to these addresses again.
Reputation Killer: High hard bounce rates (above 2%) are the fastest way to get flagged as a “spammer” by ISP filters. It suggests you are using old, scraped, or unverified lists.
2. What is a Soft Bounce?
A Soft Bounce is a temporary delivery failure. The email address is valid, but the message couldn’t get through this time.
- Common Causes: The recipient’s inbox is full, their server was temporarily down, or the email was too large.
- The Action: Sendonyx will attempt to retry sending to these addresses for a limited period. If an address continues to soft bounce over multiple campaigns, it is best practice to remove it manually.
3. Bounce Rate Benchmarks
How do you know if your list is “healthy”? Use these numbers as a guide:
| Rate | Status | Action Needed |
| Under 1% | ✅ Excellent | Keep doing what you’re doing. |
| 1% – 3% | ⚠️ Warning | Time to clean your list and check your opt-in process. |
| Above 5% | 🚨 Critical | Stop sending. Your domain is at risk of being blacklisted. |
Pro Tip: Always use a Double Opt-In (confirmation email) process. This ensures that every email on your list is valid and active from the very first second, virtually eliminating hard bounces.