SMTP 221 Closing Connection vs 500 Syntax Error
SMTP 221 (Closing Connection) is a 2xx Positive Completion response, while 500 (Syntax Error) is a 5xx Permanent Negative response. 221 indicates that the server is closing the transmission channel. This is the normal response to the QUIT command, indicating a graceful end to the SMTP session. 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.
描述
The server is closing the transmission channel. This is the normal response to the QUIT command, indicating a graceful end to the SMTP session.
何时出现
After sending the QUIT command at the end of a mail session. The server acknowledges the disconnect and the TCP connection will be closed.
如何修复
No fix needed — this is the expected response when ending an SMTP session. If you see this unexpectedly, the server may be shutting down or timing out idle connections.
描述
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.
何时出现
When you send a command the server does not understand — often due to a typo, unsupported command, or an excessively long line.
如何修复
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.
主要区别
221 is a 2xx Positive Completion response, while 500 is a 5xx Permanent Negative response.
SMTP 221: The server is closing the transmission channel. This is the normal response to the QUIT command, indicating a graceful end to the SMTP session.
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 221 when after sending the QUIT command at the end of a mail session. The server acknowledges the disconnect and the TCP connection will be closed.
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.
何时使用哪个
For 221 (Closing Connection): No fix needed — this is the expected response when ending an SMTP session. If you see this unexpectedly, the server may be shutting down or timing out idle connections. 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.