What to do
- Use an app password or OAuth.
How it appears in a bounce
550 5.7.8 Authentication credentials invalidPaste the full bounce into the decoder — it finds every code and recipient and says what to check.
SMTP 5.7.8 Authentication credentials invalid
Wrong login or password (Gmail: “Username and Password not accepted”).
5.7.8
- Class
- 5xx · Permanent failure
- Retried?
- No, the message bounces
- Defined in
- RFC 3463