A soft bounce occurs when an email cannot be delivered to the recipient due to a temporary issue, such as a full inbox or a temporary server problem. Unlike hard bounces, soft bounces may succeed if the email is resent later.
What Is a Soft Bounce?
A soft bounce is an email delivery failure caused by temporary conditions. The recipient’s email address is valid, and the domain exists, but something prevents the message from being delivered at that moment.
Common reasons for soft bounces include:
- Mailbox is full: The recipient’s storage limit has been reached
- Temporary server issues: The receiving mail server is down or busy
- Message size limits: The email exceeds the allowed size for attachments or content
- Greylisting policies: The recipient’s server temporarily rejects the message as an anti-spam measure
Email servers often attempt to deliver messages that result in a soft bounce multiple times before giving up.
How Does a Soft Bounce Work?
When an email is sent:
- The sending mail server tries to deliver the message
- The recipient’s server accepts the connection but returns a temporary error code (such as 421 or 450)
- The sending server queues the email for retry, often for up to 72 hours
- If the message still cannot be delivered, it may eventually be classified as a hard bounce
Why Is a Soft Bounce Important?
Monitoring soft bounces matters because:
- Indicates temporary issues: Helps identify problems that may resolve without intervention
- Protects sender reputation: High soft bounce rates could signal engagement or deliverability problems
- Improves campaign performance: Understanding bounce patterns helps optimize send times and content size
- Supports list hygiene: Repeated soft bounces from the same address can indicate inactive or problematic recipients
Common Use Cases
Soft bounce analysis is used for:
- Campaign performance tracking: Monitoring delivery success rates
- Deliverability optimization: Identifying server-related or message-size issues
- Reputation management: Detecting recurring problems that might harm sender credibility
- Email throttling strategies: Adjusting retry attempts and send frequencies based on bounce patterns
FAQs About Soft Bounce
What is the difference between a soft bounce and a hard bounce?
A soft bounce is temporary, while a hard bounce is permanent and requires removing the address from your list.
Do soft bounces affect sender reputation?
Yes. While less harmful than hard bounces, a high number of soft bounces can still impact reputation and deliverability.
How can soft bounces be minimized?
By validating email addresses, optimizing email size, and monitoring server response codes to resolve technical issues.
