Microsoft 365 5.7.12
Sender was not authenticated by organization
Microsoft 365 5.7.12 means: sender was not authenticated by organization. It is a permanent failure, so do not retry it unchanged. The fix is in the sending or receiving configuration named above, not in the list. Fix that, then resend.
Microsoft 365’s exact wording
Quoted from Microsoft Learn: Email non-delivery reports and SMTP errors in Exchange Online, checked 2026-11-05. Placeholders are Microsoft 365’s own.
Provider's description
Sender was not authenticated by organization
Possible cause
The sender's message is rejected because the recipient address is set up to reject messages sent from outside its organization. Only an email administrator for the recipient's organization can change this configuration.
| Who sends it | Microsoft 365, Exchange Online and Outlook.com |
|---|---|
| Basic code | Microsoft 365 lists the enhanced code only |
| Enhanced code | 5.7.12: A password transition is needed |
| Permanent or temporary | Permanent (5xx) |
| Verifying the list prevents it | No |
In practice
550 5.7.12 Sender was not authenticated by organization means the recipient address is set to reject mail from outside its organisation. Related codes 5.7.133, 5.7.134, 5.7.135 and 5.7.136 apply the same restriction to groups, mailboxes, public folders and mail users. Only the recipient's administrator can change it. Contact the person through another channel or address. This code says nothing about your reputation or authentication; resending changes nothing.
What the sender should do
The fix is in the sending or receiving configuration named above, not in the list. Fix that, then resend.
Would verifying the list have prevented Microsoft 365 5.7.12?
No
This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
Common questions
- What does Microsoft 365 5.7.12 mean?
- Microsoft 365 5.7.12 means: sender was not authenticated by organization. It is a permanent failure, so do not retry it unchanged. The fix is in the sending or receiving configuration named above, not in the list. Fix that, then resend.
- Should I retry after Microsoft 365 5.7.12?
- No. It is a permanent (5xx) failure, so the same message to the same address will fail again. Fix the cause first. The fix is in the sending or receiving configuration named above, not in the list. Fix that, then resend.
- Would verifying my list have prevented Microsoft 365 5.7.12?
- No. This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
Sources
- Microsoft Learn: Email non-delivery reports and SMTP errors in Exchange Online (checked 2026-11-05)
- IANA: SMTP Enhanced Status Codes registry (checked 2026-11-05)
Registry and provider wording is quoted exactly; guidance is written by the SimpleVerifier Team.
SimpleVerifier Team · Last checked against the sources 2026-11-05