Is 5.7.1 always a spam block?

Not always. In corporate environments (like Exchange), it frequently means you don't have permission to email a specific internal group alias.

How do I get off a blacklist?

Identify which blacklist you are on using a blacklist checker, fix the issue that caused the listing (e.g., compromised account sending spam), and follow their specific delisting process.

← Error library

550 5.7.1 Policy / spam block

permanent Policy

Meaning

The receiving server rejected your message due to a security policy, often because it was classified as spam, your sender reputation is poor, or you lack permission to email the recipient.

Common causes

Your sending IP or domain is on a blacklist (e.g., Spamhaus).
Your email failed SPF, DKIM, or DMARC authentication checks.
The recipient is a restricted distribution list that does not accept external emails.
The message content triggered the recipient's anti-spam filters.

How to fix

Verify your SPF, DKIM, and DMARC records are correctly configured.
Check your sending IP and domain against major blacklists and request delisting if necessary.
If sending to a corporate group, contact the IT admin to grant you permission to send to that distribution list.
Review the exact bounce message text, as providers usually include a link with specific remediation steps.

Provider notes

Microsoft 365. Commonly means 'Delivery not authorized' (e.g., sending to a restricted distribution group) or 'Client host blocked using Blocklist'.

Gmail. Often accompanied by a message stating the email violates Google's recommended sender guidelines or contains suspicious content.

Example bounce

550 5.7.1 Service unavailable; Client host [192.0.2.1] blocked using Spamhaus.

FAQ

Is 5.7.1 always a spam block?: Not always. In corporate environments (like Exchange), it frequently means you don't have permission to email a specific internal group alias.
How do I get off a blacklist?: Identify which blacklist you are on using a blacklist checker, fix the issue that caused the listing (e.g., compromised account sending spam), and follow their specific delisting process.