Enhanced SMTP status code · RFC 3463 · IANA
5.7.144 XOAUTH2 authentication failed
The OAuth token lacks the right permissions for the HVE application.
- 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).
- Subject: X.7 · Security and policy
Policies (per-host or per-recipient filters) and cryptographic operations; up to the sender, the recipient or both.
How 5.7.144 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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535 5.7.144
XOAUTH2 authentication failed. Invalid API permissions.
The OAuth token lacks the right permissions for the HVE application.
Have the whole error message?
Sources: RFC 5321 · RFC 3463 · RFC 3464 · IANA · Gmail · Microsoft 365 · read on 26 September 2026