SMTP 211 System Status vs 550 Mailbox Not Found
SMTP 211 (System Status) is a 2xx Positive Completion response, while 550 (Mailbox Not Found) 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, 550 means that the requested action was not taken because the mailbox does not exist or the recipient address is rejected by policy. This is a permanent failure indicating the address is invalid or blocked.
คำอธิบาย
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.
เมื่อคุณพบเห็น
When querying the mail server for its status or capabilities. The server is sharing diagnostic or informational details about itself.
วิธีแก้ไข
No fix needed — this is an informational response. If the status indicates a problem, review the server's configuration or contact the mail administrator.
คำอธิบาย
The requested action was not taken because the mailbox does not exist or the recipient address is rejected by policy. This is a permanent failure indicating the address is invalid or blocked.
เมื่อคุณพบเห็น
When sending to an email address that does not exist on the destination server, or when the server's policy rejects your message (e.g., anti-spam, sender verification failure).
วิธีแก้ไข
Verify the recipient's email address for typos. If the address is correct, the mailbox may have been deleted or your domain may be blocked — check your sender reputation and SPF/DKIM/DMARC records.
ความแตกต่างหลัก
211 is a 2xx Positive Completion response, while 550 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 550: The requested action was not taken because the mailbox does not exist or the recipient address is rejected by policy. This is a permanent failure indicating the address is invalid or blocked.
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 550 when when sending to an email address that does not exist on the destination server, or when the server's policy rejects your message (e.g., anti-spam, sender verification failure).
ควรใช้อันไหนเมื่อไร
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 550 (Mailbox Not Found): Verify the recipient's email address for typos. If the address is correct, the mailbox may have been deleted or your domain may be blocked — check your sender reputation and SPF/DKIM/DMARC records.