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SMTP codes

SMTP 535 Authentication credentials invalid

Wrong login or password, or the provider blocks basic authentication for this account.

535
Class
5xx · Permanent failure
Retried?
No, the message bounces
Defined in
RFC 4954

What to do

How it appears in a bounce

535 Authentication credentials invalid

Paste the full bounce into the decoder — it finds every code and recipient and says what to check.

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