When doing email marketing, some status codes will be returned in the log to inform whether the email is sent successfully, similar to the status code in the header when visiting a website , 404 means the page does not exist, etc. The status code 2.0.0 of the sent mail indicates successful delivery, and the soft Bounce and Hard Bounce status codes we often talk about are summarized as follows:
| Bounce code | Bounce type | Description |
| 5.0.0 | Hard | Address does not exist |
| 5.1.0 | Hard | Other address status |
| 5.1.1 | Hard | Bad destination mailbox address |
| 5.1.2 | Hard | Bad destination system address |
| 5.1.3 | Hard | Bad destination mailbox address syntax |
| 5.1.4 | Hard | Destination mailbox address ambiguous |
| 5.1.5 | Hard | Destination mailbox address valid |
| 5.1.6 | Hard | Mailbox has moved |
| 5.1.7 | Hard | Bad sender’s mailbox address syntax |
| 5.1.8 | Hard | Bad sender’s system address |
| 5.2.0 | Soft | Other or undefined mailbox status |
| 5.2.1 | Soft | Mailbox disabled, not accepting messages |
| 5.2.2 | Soft | Mailbox full |
| 5.2.3 | Hard | Message length exceeds administrative limit. |
| 5.2.4 | Hard | Mailing list expansion problem |
| 5.3.0 | Hard | Other or undefined mail system status |
| 5.3.1 | Soft | Mail system full |
| 5.3.2 | Hard | System not accepting network messages |
| 5.3.3 | Hard | System not capable of selected features |
| 5.3.4 | Hard | Message too big for system |
| 5.4.0 | Hard | Other or undefined network or routing status |
| 5.4.1 | Hard | No answer from host |
| 5.4.2 | Hard | Bad connection |
| 5.4.3 | Hard | Routing server failure |
| 5.4.4 | Hard | Unable to route |
| 5.4.5 | Soft | Network congestion |
| 5.4.6 | Hard | Routing loop detected |
| 5.4.7 | Hard | Delivery time expired |
| 5.5.0 | Hard | Other or undefined protocol status |
| 5.5.1 | Hard | Invalid command |
| 5.5.2 | Hard | Syntax error |
| 5.5.3 | Soft | Too many recipients |
| 5.5.4 | Hard | Invalid command arguments |
| 5.5.5 | Hard | Wrong protocol version |
| 5.6.0 | Hard | Other or undefined media error |
| 5.6.1 | Hard | Media not supported |
| 5.6.2 | Hard | Conversion required and prohibited |
| 5.6.3 | Hard | Conversion required but not supported |
| 5.6.4 | Hard | Conversion with loss performed |
| 5.6.5 | Hard | Conversion failed |
| 5.7.0 | Hard | Other or undefined security status |
| 5.7.1 | Hard | Delivery not authorized, message refused |
| 5.7.2 | Hard | Mailing list expansion prohibited |
| 5.7.3 | Hard | Security conversion required but not possible |
| 5.7.4 | Hard | Security features not supported |
| 5.7.5 | Hard | Cryptographic failure |
| 5.7.6 | Hard | Cryptographic algorithm not supported |
| 5.7.7 | Hard | Message integrity failure |
| 9.1.1 | Hard | Hard bounce with no bounce code found. It could be an invalid email or rejected email from your mail server (such as from a sending limit). |
