In this world, there are many domains used to send and receive email. When an email bounces, it depends on the conditions of the recipient's domain and mail server, which is why the reasons for the bounce will vary and differ from each other.
We group these bounce reasons into bounce classifications based on the general code below:
| Clasification | Name | Description | Category |
|---|---|---|---|
| 10 | Invalid Recipient | The recipient is invalid. | Hard |
| 20 | Soft Bounce | The message soft bounced. | Soft |
| 21 | DNS Failure | The message bounced due to a DNS failure. | Soft |
| 22 | Mailbox Full | The message bounced due to the remote mailbox being over quota. | Soft |
| 23 | Too Large | The message bounced because it was too large for the recipient. | Soft |
| 24 | Timeout | The message timed out. | Soft |
| 30 | Generic Bounce: No RCPT | No recipient could be determined for the message. | Hard |
| 40 | Generic Bounce | The message failed for unspecified reasons. | Soft |
| 50 | Failure | 554 5.7.1 recipient address was suppressed due to system policy | Hard |
| 60 | Auto-Reply | The message is an auto-reply/vacation mail. | Soft |
| 90 | Unsubscribe | The message is an unsubscribe request. | Hard |
Soft bounces are typically temporary events, indicating that the email delivery issue is likely to be resolved in the near future. These bounces usually result from temporary problems with the recipient's mailbox, mail server, or network, and the email may still be delivered successfully in subsequent attempts.
Soft bounces differ from hard bounces, which are permanent events indicating that the email could not be delivered due to a permanent issue with the recipient's email address or domain. Understanding the distinction between soft and hard bounces is crucial for effective email deliverability management and optimizing the success of email campaigns.