What is Proofpoint?

Proofpoint is an enterprise security company that provides email protection for many Fortune 500 companies, government agencies, and notably powers Apple iCloud Mail's spam filtering. Unlike traditional public DNSBLs, Proofpoint operates as a commercial filtering service with its own dynamic reputation system.

Impact Level: Very High for enterprise delivery. If you're sending to corporate recipients, especially large organizations, Proofpoint is likely in the path. Their filtering of iCloud Mail means consumer impact as well.

How Proofpoint works:

• Dynamic reputation: IP and domain reputation calculated continuously based on global threat intelligence
• Content analysis: Advanced scanning of message content, attachments, and URLs
• Machine learning: Behavioral analysis detecting anomalies and campaign patterns
• User reporting: Spam reported by Proofpoint-protected users feeds into reputation

What triggers filtering:

• Sending patterns resembling spam campaigns
• Poor engagement metrics from recipients at protected organizations
• Links to suspicious or newly registered domains
• Authentication failures or misalignment
• Content matching known threat patterns

How to check: Proofpoint doesn't offer a public lookup tool. You'll know you're blocked when you see deferrals or bounces referencing Proofpoint in SMTP responses (often containing "pphosted.com" or error codes like "421 4.7.1").

Remediation: Proofpoint filtering is largely automated and reputation-based. There's no public "delist" form. For enterprise senders with persistent issues, contact Proofpoint Support. Focus on:

1. Reducing complaint rates and improving engagement
2. Ensuring proper authentication
3. Cleaning your lists and warming new IPs/domains properly
4. For persistent issues, larger senders can contact Proofpoint's sender relations team

Proofpoint guards some of the most valuable cargo in the digital world. They don't publish a blocklist because they don't need to - they simply close the harbor gates based on what their intelligence network tells them.