# 550 5.7.1 服务不可用；客户端主机 [x.x.x.x] 被 Spamhaus 阻止

- **ID:** `communication/smtp-550-spamhaus-blocked`
- **领域:** communication
- **类别:** auth_error
- **错误码:** `550`
- **验证级别:** ai_generated
- **修复率:** 78%

## 根因

发送 IP 地址被列入 Spamhaus 阻止列表（SBL）或漏洞利用阻止列表（XBL），导致接收 MTA 拒绝连接，视为垃圾邮件。

## 版本兼容性

| 版本 | 状态 | 引入 | 弃用 |
|------|------|------|------|
| Postfix 3.8 | active | — | — |
| Sendmail 8.17 | active | — | — |
| Exim 4.96 | active | — | — |
| Spamhaus SBL v2 | active | — | — |

## 解决方案

1. ```
   Check the IP against Spamhaus using: `dig +short x.x.x.x.zen.spamhaus.org`. If listed, visit https://www.spamhaus.org/lookup/ to request delisting after fixing the spam issue (e.g., securing the server from being an open relay).
   ```
2. ```
   Route outgoing mail through a trusted SMTP relay or service (e.g., SendGrid, AWS SES) that has a clean IP reputation. Configure Postfix: `relayhost = [smtp.sendgrid.net]:587` with credentials.
   ```
3. ```
   If the IP is static, contact the ISP or hosting provider to request a new IP address and update DNS records accordingly.
   ```

## 无效尝试

- **Change the sender email domain to a different one** — Changing the sending domain does not affect the IP reputation; the block is based on the IP address, not the domain. (92% 失败率)
- **Add SPF and DKIM records to the sending domain** — Adding SPF/DKIM records does not remove the IP from the blocklist; the block is at the IP level and requires delisting. (88% 失败率)
- **Restart the SMTP server (Postfix/Sendmail)** — Restarting the MTA does not change the IP's blocklist status; the IP remains listed until delisting is requested. (95% 失败率)