SMTP 235 Authentication Successful vs 503 Bad Sequence
SMTP 235 (Authentication Successful) is a 2xx Positive Completion response, while 503 (Bad Sequence) is a 5xx Permanent Negative response. 235 indicates that the client has been successfully authenticated using the AUTH command. The server will now accept mail commands from this authenticated session. In contrast, 503 means that the commands were sent in the wrong order. SMTP requires a specific command sequence (EHLO, MAIL FROM, RCPT TO, DATA) and this error indicates a step was skipped or repeated.
Описание
The client has been successfully authenticated using the AUTH command. The server will now accept mail commands from this authenticated session.
Когда вы это видите
After submitting valid credentials via the AUTH command (LOGIN, PLAIN, or other SASL mechanism). The server has verified your identity and you can now send mail.
Как исправить
No fix needed — authentication succeeded. If you expected this but received a different code, double-check your username, password, and the authentication mechanism.
Описание
The commands were sent in the wrong order. SMTP requires a specific command sequence (EHLO, MAIL FROM, RCPT TO, DATA) and this error indicates a step was skipped or repeated.
Когда вы это видите
When sending DATA before RCPT TO, or MAIL FROM before EHLO. The server enforces the correct SMTP command sequence and you have sent a command out of order.
Как исправить
Follow the proper SMTP command sequence: EHLO/HELO first, then MAIL FROM, then RCPT TO (one or more), then DATA. Reset with RSET if you need to start over.
Ключевые различия
235 is a 2xx Positive Completion response, while 503 is a 5xx Permanent Negative response.
SMTP 235: The client has been successfully authenticated using the AUTH command. The server will now accept mail commands from this authenticated session.
SMTP 503: The commands were sent in the wrong order. SMTP requires a specific command sequence (EHLO, MAIL FROM, RCPT TO, DATA) and this error indicates a step was skipped or repeated.
You encounter 235 when after submitting valid credentials via the AUTH command (LOGIN, PLAIN, or other SASL mechanism). The server has verified your identity and you can now send mail.
You encounter 503 when when sending DATA before RCPT TO, or MAIL FROM before EHLO. The server enforces the correct SMTP command sequence and you have sent a command out of order.
Когда что использовать
For 235 (Authentication Successful): No fix needed — authentication succeeded. If you expected this but received a different code, double-check your username, password, and the authentication mechanism. For 503 (Bad Sequence): Follow the proper SMTP command sequence: EHLO/HELO first, then MAIL FROM, then RCPT TO (one or more), then DATA. Reset with RSET if you need to start over.