5.7.510 Microsoft bounce: recipient refuses ipv6 mail
What 5.7.510 means
You sent over IPv6, but the recipient domain does not accept inbound mail over IPv6.
Message text
Access denied, [recipient domain] does not accept email over IPv6
Common causes of 5.7.510
- Sending server connected to the recipient over IPv6
- Recipient domain does not accept IPv6 inbound mail
How to fix 5.7.510
- Check the recipient domain's MX hosts with MX lookup to see which addresses they publish.
- Ask the recipient administrator whether they accept inbound mail over IPv6.
- Send over an IPv4 path to that recipient, for example through an IPv4 relay.
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How to read 5.7.510
The second part, 5.7.510, is an enhanced status code (RFC 3463 §2) written class.subject.detail. Class 5 is a Permanent failure (5xx): the command was rejected and the sender should not repeat it unchanged (RFC 5321 §4.2.1; RFC 3463 §2).. Subject 7 is security or policy: authentication, authorization or policy refused the message. The detail number refines the subject, and providers may define details of their own, which is why one code can read differently at Gmail, Microsoft and Yahoo.
Do not keep resending the same message: a permanent failure repeats until the cause is fixed. Correct the cause, then send a new message.
Official source: learn.microsoft.com. Last verified 2026-10-20.
Related guides
- How to create an SPF record (syntax and examples)
- How DKIM works and how to publish a DKIM record
- How to set up a DMARC record, from p=none to p=reject
Related codes
- 5.7.0 SMTP: security status
- 5.7.1 SMTP: delivery not authorized
- 5.7.23 SMTP: SPF validation failed
- 5.7.25 SMTP: reverse DNS failed
- 5.7.26 SMTP: authentication failed
- 5.7.27 SMTP: sender has null MX
FAQ
What does 5.7.510 mean?
You sent over IPv6, but the recipient domain does not accept inbound mail over IPv6. This is a permanent failure.
How do I fix 5.7.510?
Check the recipient domain's MX hosts with MX lookup to see which addresses they publish. Ask the recipient administrator whether they accept inbound mail over IPv6. Send over an IPv4 path to that recipient, for example through an IPv4 relay.
Is 5.7.510 permanent, and should I retry?
5.7.510 is a permanent failure, so retrying the same message will fail again. Fix the cause first, then send a new message.