A hard bounce occurs when an email cannot be delivered to the recipient due to a permanent reason, such as an invalid email address or a nonexistent domain. Hard bounces indicate addresses that should be removed from your email list immediately.
What Is a Hard Bounce?
A hard bounce is an email delivery failure that signals a permanent issue. Unlike soft bounces, which are temporary (for example, a full inbox or server outage), hard bounces happen because the email address or domain is invalid and will never accept emails.
Common causes of hard bounces include:
- Invalid email addresses: The address was typed incorrectly or no longer exists
- Non-existent domains: The domain name is inactive or has expired
- Blocked emails: The recipient’s mail server has permanently blocked your messages
High hard bounce rates damage sender reputation, as ISPs view them as a sign of poor list hygiene.
How Does a Hard Bounce Work?
When you send an email:
- The sending server attempts to deliver the message to the recipient’s mail server
- If the mail server cannot find the address or domain, it returns a permanent error code (typically 550)
- The email is marked as a hard bounce and is not retried for future delivery
Most email service providers automatically suppress hard-bounced addresses to prevent repeated delivery attempts.
Why Is Hard Bounce Important?
Understanding hard bounces is critical because:
- Protects sender reputation: High hard bounce rates can cause ISPs to block your domain or IP
- Improves deliverability: Reducing invalid addresses lowers overall bounce rates
- Saves money: Prevents wasted resources on emails that cannot be delivered
- Ensures compliance: Helps maintain standards required by email marketing platforms and ISPs
Common Use Cases
Hard bounce data is used for:
- Email list cleaning: Removing invalid addresses to maintain list quality
Performance monitoring: Identifying campaigns that target poor-quality data
Reputation management: Preventing penalties from ISPs and email providers
Risk scoring: Flagging addresses that are likely to result in future delivery failures
FAQs About Hard Bounce
What causes a hard bounce?
A hard bounce occurs when an email address is invalid, the domain does not exist, or the recipient server has blocked your emails permanently.
How is a hard bounce different from a soft bounce?
A hard bounce is a permanent failure, while a soft bounce is temporary and might resolve later.
How can hard bounces be reduced?
You can reduce hard bounces by validating email addresses with tools like Listmint before sending campaigns and removing invalid addresses from your list.
