A high number of hard bounces (greater than 4%) is a sign of list quality issues and can hurt your sender reputation. In this article, you’ll learn the common causes of hard bounces and the steps you can take to reduce them.
What Are Hard Bounces?
A hard bounce occurs when an email cannot be delivered because the address is invalid. This could mean:
The email address never existed.
The mailbox is no longer active.
The domain is invalid.
When mailbox providers see high bounce rates, they may assume poor data hygiene or even spammer-like behavior (e.g., dictionary attacks, where spammers generate random email combinations to find valid addresses).
Common Causes of High Hard Bounces
Sending to old or outdated lists.
Sending to an opt-out list.
Mailbox providers deactivating inactive addresses.
How to Reduce Hard Bounces
Verify Email Addresses at Opt-in
Make sure your opt-in system validates email addresses during signup.
Use double opt-in to confirm subscribers are real.
Use List Analysis and Verification
Use Emercury Clean + Analyze service to remove spam traps and hard bounces.
Alternatively, use a trusted third-party email verification service before sending.
Mail Regularly
Contact your subscribers at least once per quarter to keep your list fresh.
Inactive lists are more likely to generate bounces.
Test Before Full Sends
Mail to a sample segment first to measure bounce rates.
If bounces are high, clean the list before sending to the entire group.
Work with your Customer Success manager
If bounce rates remain high, inquire about additional email verification services or custom list-cleaning strategies.
By following these practices, you’ll reduce hard bounces, improve deliverability, and maintain a stronger sending reputation.