SMTP 252 Cannot Verify User vs 550 Mailbox Not Found
SMTP 252 (Cannot Verify User) is a 2xx Positive Completion response, while 550 (Mailbox Not Found) is a 5xx Permanent Negative response. 252 indicates that the server cannot verify the user but will accept the message and attempt delivery. This is often returned in response to VRFY when the server intentionally hides user information. 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.
Descrição
The server cannot verify the user but will accept the message and attempt delivery. This is often returned in response to VRFY when the server intentionally hides user information.
Quando você o vê
When using the VRFY command to check if a recipient exists. The server refuses to confirm or deny the address, typically as a spam-prevention measure.
Como corrigir
No fix needed — the server will still attempt delivery. If you need to verify addresses, contact the mail administrator or rely on bounce-back messages instead.
Descrição
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.
Quando você o vê
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).
Como corrigir
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.
Diferenças principais
252 is a 2xx Positive Completion response, while 550 is a 5xx Permanent Negative response.
SMTP 252: The server cannot verify the user but will accept the message and attempt delivery. This is often returned in response to VRFY when the server intentionally hides user information.
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 252 when when using the VRFY command to check if a recipient exists. The server refuses to confirm or deny the address, typically as a spam-prevention measure.
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).
Quando usar qual
For 252 (Cannot Verify User): No fix needed — the server will still attempt delivery. If you need to verify addresses, contact the mail administrator or rely on bounce-back messages instead. 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.