Enhanced status codes are structured as class.subject.detail.
Common subjects include:
| Subject | General area |
|---|---|
| X.1.x | Addressing |
| X.2.x | Mailbox |
| X.3.x | Mail system |
| X.4.x | Network/routing |
| X.5.x | Mail delivery protocol |
| X.6.x | Message content/media |
| X.7.x | Security or policy |
The exact detail matters. Do not treat every 5.7.x response as the same reputation block.