When an email cannot be delivered after several attempts, a bounce is generated. There are two types: soft bounce and hard bounce. This article explains the difference between the two and what you can do in each case.
Hover over the Soft bounce or Hard bounce status label in the Activity tab to display the reason for the issue directly in the list.
Soft bounce
A soft bounce means that delivery of the message permanently failed after several attempts, for a reason that was temporary in nature. The system will no longer make automatic retry attempts. The recipient did not receive the message. You may choose to resend it manually if you believe the issue has been resolved.
Possible causes:
- The recipient's inbox is full
- The recipient's mail server was temporarily unavailable or overloaded
- The recipient's server imposed temporary limits on incoming messages
- The recipient's server applies greylisting — an anti-spam technique that temporarily refuses messages from an unknown sender. The sending service exhausted its attempts before the message was accepted
- The message content was detected as spam by the recipient's server
- A reputation issue related to the sending IP address or domain
Hard bounce
A hard bounce means that delivery of the message failed permanently. The recipient will never receive the message. It is a final status that will not change.
Possible causes:
- The email address does not exist, is invalid, has been closed, deleted, or is deactivated
- The recipient's domain does not exist or does not accept emails
- The recipient's server permanently refuses the message
Summary
| Soft bounce | Hard bounce | |
|---|---|---|
| Nature of the issue | Temporary, but attempts exhausted | Permanent |
| Automatic retries | No — exhausted | No |
| Final status | Yes | Yes |
| Recommended action | Resend manually if relevant | Verify or remove the address |
What to do depending on the type of bounce
Soft bounce
The system will no longer make automatic retry attempts. If you believe the issue has been resolved (e.g., a full inbox has been cleared, a server has been restored), you can resend the message manually from your application.
Hard bounce
Verify that the recipient's address is valid and that the domain exists before attempting a new mailing. Avoid resending messages to an address that generates hard bounces — this could damage the reputation of your sending domain and affect the deliverability of your future mailings.
See also: