SMTP 334 Server Challenge vs 500 Syntax Error
SMTP 334 (Server Challenge) is a 3xx Positive Intermediate response, while 500 (Syntax Error) is a 5xx Permanent Negative response. 334 indicates that the server is issuing an authentication challenge as part of the SASL authentication exchange. The response contains a Base64-encoded challenge that the client must decode and respond to. In contrast, 500 means that the server could not recognize the command due to a syntax error. The command line was malformed or the command is not recognized by this server.
説明
The server is issuing an authentication challenge as part of the SASL authentication exchange. The response contains a Base64-encoded challenge that the client must decode and respond to.
このコードが表示される場合
During the AUTH command handshake. The server is prompting you for your username or password (Base64-encoded) as part of the multi-step authentication process.
解決方法
Respond with the appropriate Base64-encoded credentials. If authentication keeps failing after responding, verify your credentials and ensure you are using the correct SASL mechanism.
説明
The server could not recognize the command due to a syntax error. The command line was malformed or the command is not recognized by this server.
このコードが表示される場合
When you send a command the server does not understand — often due to a typo, unsupported command, or an excessively long line.
解決方法
Check the command spelling and syntax against the SMTP specification. Ensure the command line does not exceed 512 characters and uses proper CRLF line endings.
主な違い
334 is a 3xx Positive Intermediate response, while 500 is a 5xx Permanent Negative response.
SMTP 334: The server is issuing an authentication challenge as part of the SASL authentication exchange. The response contains a Base64-encoded challenge that the client must decode and respond to.
SMTP 500: The server could not recognize the command due to a syntax error. The command line was malformed or the command is not recognized by this server.
You encounter 334 when during the AUTH command handshake. The server is prompting you for your username or password (Base64-encoded) as part of the multi-step authentication process.
You encounter 500 when when you send a command the server does not understand — often due to a typo, unsupported command, or an excessively long line.
どちらをいつ使うか
For 334 (Server Challenge): Respond with the appropriate Base64-encoded credentials. If authentication keeps failing after responding, verify your credentials and ensure you are using the correct SASL mechanism. For 500 (Syntax Error): Check the command spelling and syntax against the SMTP specification. Ensure the command line does not exceed 512 characters and uses proper CRLF line endings.