550 5.7.1 Email Rejected — How to Fix It

What 550 5.7.1 Means

The 550 SMTP status code means "Requested action not taken: mailbox unavailable." The 5.7.1 sub-code specifically means the message was rejected due to policy reasons — not because the mailbox doesn't exist, but because the server chose to reject it.

Unlike soft bounces (4xx codes, which are temporary), a 550 is a hard permanent rejection. Most email systems will stop retrying after a 550.

Common Causes and Fixes

1. SPF or DMARC Policy Rejection

The most common cause. The receiving server's spam filter checked your SPF record and found the sending IP isn't authorized, or your DMARC policy says to reject unauthorized senders.

Fix: Check your SPF record includes your sending server's IP or your ESP's include directive. Verify DMARC alignment — if your DMARC is p=reject and you're failing SPF alignment without DKIM, emails will be rejected.

2. Sending IP on a Blacklist

Major providers (Gmail, Outlook, Yahoo) check Spamhaus and other DNSBLs on every inbound connection. A listing on a critical blacklist causes immediate 550 rejection.

The bounce message often includes the blacklist name: "Your message was rejected because the IP 1.2.3.4 is listed on Spamhaus ZEN."

Fix: Check your sending IP with the Blacklist Checker. Follow the delist links for any listings found.

3. Recipient Domain Blocks Your IP or Domain

Some organizations run their own blocklists. If you've been reported for spam by someone at that organization, their mail server may be blocking all email from your domain or IP.

Fix: Contact their postmaster (abuse@theirdomain.com) and request removal. Include information about your sending practices.

4. Missing or Invalid Reverse DNS (PTR Record)

Many mail servers require the sending IP to have a valid PTR record (reverse DNS) that matches the hostname used in the SMTP greeting. Without it, some servers reject with 550.

Fix: Ask your hosting provider to set a PTR record for your mail server's IP. The PTR should resolve to your mail server's hostname, and that hostname should resolve back to the same IP.

5. Content Filtering

The email content triggered a rule severe enough for rejection rather than just spam scoring. Executable attachments (.exe, .js), password-protected ZIPs, and certain URL patterns often cause immediate 550 rejection.