What the message looks like
550 5.7.1 Message rejected due to local policy550 5.7.1 [CS01] Message rejected due to local policy550-5.7.1 Gmail has detected that this message is likely unsolicited mail550 5.7.1 Recipient address rejected: Recipient not found550 5.7.1 Unable to relay
What it means
The receiving server refused the email because of one of its own rules. The standard name for this status is "delivery not authorized, message refused". It's a catch-all code, so the text after it matters more than the number.
Common causes
- The email looked like spam or phishing to the receiving server's filters.
- The sender's IP address or domain is on a blocklist.
- The recipient, or their organisation, has blocked the sender.
- The receiving server only accepts mail from certain senders, such as a company that blocks outside email to some addresses. Microsoft 365 groups that only accept internal senders reject outside email with
5.7.133"not authenticated for group". - The email is badly formed, such as a missing Message-ID or more than one From header. Gmail rejects these as "not RFC 5322 compliant", and Microsoft uses
5.7.512. - The sending server tried to relay mail through a server it isn't allowed to use.
- The address doesn't exist. Some providers use 5.7.1 with wording like "Recipient not found" or "Recipient not available" instead of 550 5.1.1, so treat those like an address that doesn't exist.
Apple's iCloud Mail sends 550 5.7.1 [CS01] Message rejected due to local policy when it decides an email is spam or phishing, and Gmail sends 550-5.7.1 with "likely unsolicited mail" for the same reason. Yahoo uses 554 5.7.9 Message not accepted for policy reasons.
If you're the recipient
Check you haven't blocked the sender, and add them to your contacts or safe senders list. If your provider keeps rejecting a sender you want to hear from, contact your provider's support with the full error message.
If you're the sender
Read the full text of the error for a reason or a link. Check your domain has valid SPF, DKIM and DMARC records, and that your sending IP address isn't on a public blocklist. If you send marketing email, make sure people opted in and can unsubscribe easily.
If you use addy.io
If your inbox provider rejects an email that addy.io forwards to you, it appears on your Failed Deliveries page. This happens most with iCloud, Gmail and Outlook. Adding the alias to your contacts, encrypting forwarded emails with your GPG key, or replacing the subject can help. See I'm not receiving any emails, what's wrong?