SMTP 220 Service Ready vs 504 Parameter Not Implemented
SMTP 220 (Service Ready) is a 2xx Positive Completion response, while 504 (Parameter Not Implemented) is a 5xx Permanent Negative response. 220 indicates that the SMTP server is ready to begin the mail transaction. This greeting is the first response a client receives upon connecting, and it typically includes the server's hostname and software identificati 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.
Descripción
The SMTP server is ready to begin the mail transaction. This greeting is the first response a client receives upon connecting, and it typically includes the server's hostname and software identification.
Cuándo lo verás
Immediately after establishing a TCP connection to the mail server on port 25, 465, or 587. This is the server's welcome banner confirming it is ready to accept commands.
Cómo solucionarlo
No fix needed — this confirms a successful connection. If you do not receive this greeting, check that the server is running, the port is correct, and no firewall is blocking the connection.
Descripción
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.
Cuándo lo verás
When using SMTP extensions or parameters that the server does not support, such as an unsupported AUTH mechanism or an unrecognized MAIL FROM parameter.
Cómo solucionarlo
Check the server's EHLO response for supported extensions and parameters. Use only the mechanisms and parameters listed in the server's capability advertisement.
Diferencias clave
220 is a 2xx Positive Completion response, while 504 is a 5xx Permanent Negative response.
SMTP 220: The SMTP server is ready to begin the mail transaction. This greeting is the first response a client receives upon connecting, and it typically includes the server's hostname and software identificati
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 220 when immediately after establishing a TCP connection to the mail server on port 25, 465, or 587. This is the server's welcome banner confirming it is ready to accept commands.
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.
Cuándo usar cada uno
For 220 (Service Ready): No fix needed — this confirms a successful connection. If you do not receive this greeting, check that the server is running, the port is correct, and no firewall is blocking the connection. 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.