550 5.7.1 This message does not meet IPv6 sending guidelines regarding PTR records and authentication
Sample bounce line
550 5.7.1 This message does not meet IPv6 sending guidelines regarding PTR records and authentication. For more information, go to Email sender guidelines.
What it means
The message was sent over IPv6 and did not meet Gmail's IPv6 sending guidelines for PTR records and authentication, so it was rejected.
Why it happens
- The sending IPv6 address has no PTR (reverse DNS) record, or the PTR hostname has no matching AAAA record pointing back to the same IP.
- The sending IP does not match the IP of the hostname in its PTR record.
- The message is not authenticated with SPF or DKIM.
How to fix it
- Give the public IPv6 address of the sending SMTP server a PTR record that resolves to a hostname (reverse DNS).
- Make sure the same hostname has an AAAA record that resolves to the same public IPv6 address used by the sending server (forward DNS).
- Confirm the sending IP address matches the IP address of the hostname in the PTR record.
- Set up SPF and/or DKIM for the sending domain (DKIM key of 1024 bits or longer, 2048 recommended), and DMARC if you send 5,000 or more messages a day to Gmail.
DNS record examples (replace example.com and the values with your own):
203.0.113.25 -> mail.example.com (PTR, set by whoever owns the IP) mail.example.com. IN A 203.0.113.25 ; forward record must point back to the same IP
Check your domain now
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