Bounce Rate
Bounce rate is the percentage of sent emails that could not be delivered to the recipient's mailbox.
What Is Bounce Rate?
Email bounces fall into two categories: hard bounces and soft bounces. A hard bounce means the email address is permanently undeliverable — it doesn't exist, the domain is invalid, or the server has permanently rejected delivery. A soft bounce is a temporary delivery failure caused by a full inbox, a server outage, or a message that's too large. Bounce rate is calculated as (bounced emails ÷ total emails sent) × 100. A healthy bounce rate is below 2%. Anything above 5% is a red flag that can damage your sender reputation and trigger ISP scrutiny.
Why It Matters for Newsletters
High bounce rates signal to email providers that you're not maintaining your list properly, which can lead to your emails being flagged as spam across all recipients. This creates a downward spiral: more bounces lead to worse reputation, which leads to more emails being filtered, which reduces engagement, which further damages reputation. For newsletters, keeping bounce rates low is essential for sustainable growth.
Best Practices
- Use double opt-in to verify email addresses before adding them to your list
- Remove hard bounces immediately after the first occurrence
- Monitor soft bounces and remove addresses that consistently soft-bounce over 3-4 sends
- Validate email addresses at the point of collection using real-time verification
- Never purchase email lists — they're full of invalid and spam trap addresses
How Aldus Handles This
Aldus automatically processes bounces from Resend, immediately removing hard-bounced addresses and tracking soft bounces. After three consecutive soft bounces, an address is automatically suppressed. This keeps your list clean and your sender reputation strong without any manual work.