SMTP 421 Service Not Available vs 530 Authentication Required
SMTP 421 (Service Not Available) is a 4xx Transient Negative response, while 530 (Authentication Required) is a 5xx Permanent Negative response. 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. In contrast, 530 means that the server requires authentication before accepting mail commands. You must issue the AUTH command with valid credentials before attempting to send mail.
Description
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.
Quand vous le voyez
When connecting to a mail server that is overloaded, undergoing maintenance, or shutting down. The server cannot handle your request right now.
Comment résoudre
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.
Description
The server requires authentication before accepting mail commands. You must issue the AUTH command with valid credentials before attempting to send mail.
Quand vous le voyez
When trying to send mail through a server that requires authentication (typical for submission on port 587) without first logging in with the AUTH command.
Comment résoudre
Authenticate using the AUTH command with your username and password before sending MAIL FROM. Ensure your email client is configured with the correct SMTP credentials and authentication method.
Différences clés
421 is a 4xx Transient Negative response, while 530 is a 5xx Permanent Negative response.
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 530: The server requires authentication before accepting mail commands. You must issue the AUTH command with valid credentials before attempting to send mail.
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 530 when when trying to send mail through a server that requires authentication (typical for submission on port 587) without first logging in with the AUTH command.
Quand utiliser lequel
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 530 (Authentication Required): Authenticate using the AUTH command with your username and password before sending MAIL FROM. Ensure your email client is configured with the correct SMTP credentials and authentication method.