Bounce codes are returned by receiving email servers to inficate different reasons why an email was not delivered to the recipient. The bounce codes are submitted in the bounces report resource or the corresponding webhook.
This page might not contain the complete information for the codes. For detailed information consult RFC 3463 (Enhanced Mail System Status Codes).
The RFC specifies bounce codes beginning with 4 as softbounces (temporal problems) and bounce codes beginning with 5 as hardbounces (permanent problems). However, the error message only depends on the last two digits, thus, we define the error messages themselves as independent from the type of bounce.
| Code | Description |
|---|---|
| X.0.0 | Unknown issue |
| X.1.0 | Other address status |
| X.1.1 | Bad destination mailbox address |
| X.1.2 | Bad destination system address |
| X.1.3 | Bad destination mailbox address syntax |
| X.1.4 | Destination mailbox address ambiguous |
| X.1.5 | Destination mailbox address valid |
| X.1.6 | Mailbox has moved |
| X.1.7 | Bad sender’s mailbox address syntax |
| X.1.8 | Bad sender’s system address |
| X.2.0 | Other or undefined mailbox status |
| X.2.1 | Mailbox disabled – not accepting messages |
| X.2.2 | Mailbox full |
| X.2.3 | Message length exceeds administrative limit |
| X.2.4 | Mailing list expansion problem |
| X.3.0 | Other or undefined mail system status |
| X.3.1 | Mail system full |
| X.3.2 | System not accepting network messages |
| X.3.3 | System not capable of selected features |
| X.3.4 | Message too big for system |
| X.4.0 | Other or undefined network or routing status |
| X.4.1 | No answer from host |
| X.4.2 | Bad connection |
| X.4.3 | Routing server failure |
| X.4.4 | Unable to route |
| X.4.5 | Network congestion |
| X.4.6 | Routing loop detected |
| X.4.7 | Delivery time expired |
| X.5.0 | Other or undefined protocol status |
| X.5.1 | Invalid command |
| X.5.2 | Syntax error |
| X.5.3 | Too many recipients |
| X.5.4 | Invalid command arguments |
| X.5.5 | Wrong protocol version |
| X.6.0 | Other or undefined media error |
| X.6.1 | Media not supported |
| X.6.2 | Conversion required and prohibited |
| X.6.3 | Conversion required but not supported |
| X.6.4 | Conversion with loss performed |
| X.6.5 | Conversion failed |
| X.7.0 | Other or undefined security status |
| X.7.1 | Delivery not authorized – message refused |
| X.7.2 | Mailing list expansion prohibited |
| X.7.3 | Security conversion required but not possible |
| X.7.4 | Security features not supported |
| X.7.5 | Cryptographic failure |
| X.7.6 | Cryptographic algorithm not supported |
| X.7.7 | Message integrity failure |