5.7.12 Microsoft bounce: rejects outside senders
What 5.7.12 means
The recipient address is set up to accept mail only from inside its own organisation, so your message from outside was refused.
Message text
Sender was not authenticated by organization
Common causes of 5.7.12
- Recipient mailbox or group is configured to reject senders outside its organisation
How to fix 5.7.12
- Only the recipient organisation's email administrator can change this; ask them to allow external senders for that address.
- Check that the recipient address is correct with the sender before retrying.
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How to read 5.7.12
The second part, 5.7.12, 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 5.7.12 mean?
The recipient address is set up to accept mail only from inside its own organisation, so your message from outside was refused. This is a permanent failure.
How do I fix 5.7.12?
Only the recipient organisation's email administrator can change this; ask them to allow external senders for that address. Check that the recipient address is correct with the sender before retrying.
Is 5.7.12 permanent, and should I retry?
5.7.12 is a permanent failure, so retrying the same message will fail again. Fix the cause first, then send a new message.