SMTP 211 System Status vs 501 Syntax Error in Parameters
SMTP 211 (System Status) is a 2xx Positive Completion response, while 501 (Syntax Error in Parameters) is a 5xx Permanent Negative response. 211 indicates that a system status reply providing information about the mail server's current state. This is typically sent in response to a HELP or system inquiry command. 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.
描述
A system status reply providing information about the mail server's current state. This is typically sent in response to a HELP or system inquiry command.
何时出现
When querying the mail server for its status or capabilities. The server is sharing diagnostic or informational details about itself.
如何修复
No fix needed — this is an informational response. If the status indicates a problem, review the server's configuration or contact the mail administrator.
描述
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.
何时出现
When a command like MAIL FROM or RCPT TO has a malformed email address, missing angle brackets, or invalid characters in the arguments.
如何修复
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.
主要区别
211 is a 2xx Positive Completion response, while 501 is a 5xx Permanent Negative response.
SMTP 211: A system status reply providing information about the mail server's current state. This is typically sent in response to a HELP or system inquiry command.
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 211 when when querying the mail server for its status or capabilities. The server is sharing diagnostic or informational details about itself.
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.
何时使用哪个
For 211 (System Status): No fix needed — this is an informational response. If the status indicates a problem, review the server's configuration or contact the mail administrator. 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.