SMTP 211 System Status vs 504 Parameter Not Implemented
SMTP 211 (System Status) is a 2xx Positive Completion response, while 504 (Parameter Not Implemented) 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, 504 means that a command parameter is not implemented on this server. The command itself is valid but the specific parameter or extension you used is not supported.
Description
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.
When You See It
When querying the mail server for its status or capabilities. The server is sharing diagnostic or informational details about itself.
How to Fix
No fix needed — this is an informational response. If the status indicates a problem, review the server's configuration or contact the mail administrator.
Description
A command parameter is not implemented on this server. The command itself is valid but the specific parameter or extension you used is not supported.
When You See It
When using SMTP extensions or parameters that the server does not support, such as an unsupported AUTH mechanism or an unrecognized MAIL FROM parameter.
How to Fix
Check the server's EHLO response for supported extensions and parameters. Use only the mechanisms and parameters listed in the server's capability advertisement.
Key Differences
211 is a 2xx Positive Completion response, while 504 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 504: A command parameter is not implemented on this server. The command itself is valid but the specific parameter or extension you used is not supported.
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 504 when when using SMTP extensions or parameters that the server does not support, such as an unsupported AUTH mechanism or an unrecognized MAIL FROM parameter.
When to Use Which
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 504 (Parameter Not Implemented): Check the server's EHLO response for supported extensions and parameters. Use only the mechanisms and parameters listed in the server's capability advertisement.