SMTP 421 Service Not Available vs 455 Server Unable to Accommodate
Both SMTP 421 (Service Not Available) and 455 (Server Unable to Accommodate) belong to the 4xx Transient Negative category. 421 indicates that the SMTP service is not available and the server is closing the transmission channel. This may be sent as a greeting or during a session if the server needs to shut down. Meanwhile, 455 means that the server is currently unable to accommodate the requested parameters. This is a general temporary failure indicating the server cannot process the specific request at this time.
설명
The SMTP service is not available and the server is closing the transmission channel. This may be sent as a greeting or during a session if the server needs to shut down.
이 코드를 보게 되는 경우
When connecting to a mail server that is overloaded, undergoing maintenance, or shutting down. The server cannot handle your request right now.
해결 방법
Retry the connection after a delay. If the issue persists, check server status and resources (CPU, memory, disk). Rate limiting or greylisting may also trigger this response.
설명
The server is currently unable to accommodate the requested parameters. This is a general temporary failure indicating the server cannot process the specific request at this time.
이 코드를 보게 되는 경우
When the server temporarily cannot handle a specific aspect of your request, such as a particular extension or parameter that requires resources not currently available.
해결 방법
Retry the command later or try with different parameters. If the error persists, simplify the request or contact the server administrator to check resource availability.
주요 차이점
SMTP 421: The SMTP service is not available and the server is closing the transmission channel. This may be sent as a greeting or during a session if the server needs to shut down.
SMTP 455: The server is currently unable to accommodate the requested parameters. This is a general temporary failure indicating the server cannot process the specific request at this time.
You encounter 421 when when connecting to a mail server that is overloaded, undergoing maintenance, or shutting down. The server cannot handle your request right now.
You encounter 455 when when the server temporarily cannot handle a specific aspect of your request, such as a particular extension or parameter that requires resources not currently available.
언제 어떤 것을 사용할지
For 421 (Service Not Available): Retry the connection after a delay. If the issue persists, check server status and resources (CPU, memory, disk). Rate limiting or greylisting may also trigger this response. For 455 (Server Unable to Accommodate): Retry the command later or try with different parameters. If the error persists, simplify the request or contact the server administrator to check resource availability.