Enhanced SMTP status code · RFC 3463 · IANA
5.7.12 Password transition needed
The user must transition to the chosen mechanism, usually by authenticating once with PLAIN (RFC 4954).
- Class: Permanent failure
Class 5: a permanent failure. Resending the same message will not help: something about the message, the sender or the destination must change (RFC 3463 §3.1).
Also seen as:
4.7.12 - Subject: X.7 · Security and policy
Policies (per-host or per-recipient filters) and cryptographic operations; up to the sender, the recipient or both.
- Associated basic codes (IANA registry)
How 5.7.12 appears at providers
The exact text from the provider's documentation, as you see it in the bounce, and what it means.
Microsoft 365 / Exchange Online
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5.7.12
Sender was not authenticated by organization
The recipient (mailbox, group, public folder or mail user) accepts only messages from its own organisation. Only its administrator can change that.
Have the whole error message?
Sources: RFC 5321 · RFC 3463 · RFC 3464 · IANA · Gmail · Microsoft 365 · read on 26 September 2026