Documentation
550 5.7.1: blocked by the receiving server's policy.
The address may be perfectly valid. The receiver decided not to accept this message.
What it means
A 5.7.1 reply means "delivery not authorized": the message was refused for a policy reason rather than because the address is wrong. The reply text usually says which policy, with words such as "blocked", "denied", "blocklist", "spam" or "reputation". Codes 5.7.0 and 5.7.28 are related.
Typical codes and wording
550 5.7.1, 5.7.0, 5.7.28 ("blocked", "denied", "spam", "policy", "reputation")
Common causes
- The sending domain or IP address is on a blocklist, or has a poor reputation with that receiver.
- The content looks like spam to the receiver's filter (links, wording, attachments).
- The recipient's organisation has its own rules, such as only accepting mail from known senders.
- Too many complaints or bounces recently, which makes receivers stricter.
What to do
- Read the receiving server's text in the message's page: it normally names the reason or links to a page that explains it.
- Check that SPF, DKIM and DMARC pass for your sending domain: see the authentication guide below.
- Review the message: remove suspicious links or attachments, and make sure the sender and subject are honest.
- Do not retry until you know why. If you believe the address is valid, fix the cause first and then remove it from the suppression list.
What Mailtruss shows
Titled "The receiving server blocked the message by policy", with the receiver's words below it. It is a permanent bounce, so the address is added to your suppression list; remove it after you have fixed the cause.
Is it safe to retry?
Not until you know the reason and have fixed it.