SMTP 211 System Status vs 521 Host Does Not Accept Mail
SMTP 211 (System Status) is a 2xx Positive Completion response, while 521 (Host Does Not Accept Mail) 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, 521 means that the host does not accept mail at all. This indicates the server exists but is explicitly configured to reject all incoming email messages.
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 host does not accept mail at all. This indicates the server exists but is explicitly configured to reject all incoming email messages.
何时出现
When connecting to a server that has been intentionally configured to refuse all email, such as a domain that only sends but never receives mail.
如何修复
Verify you are connecting to the correct mail server by checking the domain's MX records. If the domain truly does not accept mail, contact the recipient through an alternative channel.
主要区别
211 is a 2xx Positive Completion response, while 521 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 521: The host does not accept mail at all. This indicates the server exists but is explicitly configured to reject all incoming email messages.
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 521 when when connecting to a server that has been intentionally configured to refuse all email, such as a domain that only sends but never receives mail.
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 521 (Host Does Not Accept Mail): Verify you are connecting to the correct mail server by checking the domain's MX records. If the domain truly does not accept mail, contact the recipient through an alternative channel.