SMTP 235 Authentication Successful vs 501 Syntax Error in Parameters
SMTP 235 (Authentication Successful) is a 2xx Positive Completion response, while 501 (Syntax Error in Parameters) 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, 501 means that the command was recognized but the parameters or arguments are syntactically invalid. The server understood what you wanted to do but could not parse the details.
説明
The client has been successfully authenticated using the AUTH command. The server will now accept mail commands from this authenticated session.
このコードが表示される場合
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.
解決方法
No fix needed — authentication succeeded. If you expected this but received a different code, double-check your username, password, and the authentication mechanism.
説明
The command was recognized but the parameters or arguments are syntactically invalid. The server understood what you wanted to do but could not parse the details.
このコードが表示される場合
When a command like MAIL FROM or RCPT TO has a malformed email address, missing angle brackets, or invalid characters in the arguments.
解決方法
Review the parameter format — email addresses should be enclosed in angle brackets (e.g., <[email protected]>). Check for stray spaces, missing colons, or encoding issues.
主な違い
235 is a 2xx Positive Completion response, while 501 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 501: The command was recognized but the parameters or arguments are syntactically invalid. The server understood what you wanted to do but could not parse the details.
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 501 when when a command like MAIL FROM or RCPT TO has a malformed email address, missing angle brackets, or invalid characters in the arguments.
どちらをいつ使うか
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 501 (Syntax Error in Parameters): Review the parameter format — email addresses should be enclosed in angle brackets (e.g., <[email protected]>). Check for stray spaces, missing colons, or encoding issues.