Jun 24, 2017

SMTP Authentication Reply-Codes

Code Meaning Issued by
Honored by
235 Authentication Succeeded yes yes
334 Text part containing the [BASE64] encoded string yes yes
432 A password transition is needed no >= 0.75
454 Temporary authentication failure yes n/a
500 Authentication Exchange line is too long no n/a
501 Malformed auth input/Syntax error yes n/a
503 AUTH command is not permitted during a mail transaction yes n/a
504 Unrecognized authentication type yes n/a
530 Authentication required Submission mode n/a
534 Authentication mechanism is to weak no no
535 Authentication credentials invalid yes yes
538 Encryption required for requested authentication mechanismno no