How to confirm if a blocklist or ISP-specific penalty is in effect?

Blocklist checks:

• MXToolbox blacklist check (multi-list)
• Spamhaus direct lookup
• Barracuda lookup
• Check both IP and domain

ISP-specific indicators:

• Bounce messages citing specific policies
• Postmaster tool warnings
• Provider-specific filter results

Testing:

• Send to seed addresses at affected ISPs
• Compare results across providers
• Check if problem is isolated or widespread

Error message analysis:

• Look for blocklist names in bounce text
• Look for policy or reputation references
• Note any remediation URLs provided

Check the banned ships registry. Contact port authorities for specific restrictions.