Exact response pattern
550 5.7.1 Service unavailable; client host blocked using SpamhausPermanentSpamhausBlocklist
What it means
The receiving system rejected the connection because the IP appears on a Spamhaus list.
Likely causes
- Compromised server or credentials.
- Direct-to-MX from a policy-listed range.
- Spam or bot activity.
Recommended response
- Identify the exact Spamhaus list.
- Stop abuse and secure the system.
- Follow the listed remediation procedure.
- Do not request removal before fixing the cause.
Operational rule: Preserve the complete SMTP response, remote hostname, sending IP, envelope sender and timestamp. Never diagnose from the three-digit code alone.