SMTP 252 Cannot Verify User vs 554 Transaction Failed
SMTP 252 (Cannot Verify User) is a 2xx Positive Completion response, while 554 (Transaction Failed) 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, 554 means that the mail transaction has failed. This is a catch-all permanent error that can occur at any point during the SMTP session, including as a rejection greeting when the server refuses all connections from
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 mail transaction has failed. This is a catch-all permanent error that can occur at any point during the SMTP session, including as a rejection greeting when the server refuses all connections from your IP.
Quando você o vê
When the entire mail transaction is rejected — often due to spam filtering, blacklisted IP addresses, malformed messages, or policy violations detected during the DATA phase.
Como corrigir
Check your IP against DNS blacklists (DNSBL) and verify your SPF, DKIM, and DMARC records. Review the full error message for specific rejection reasons. If blacklisted, request delisting from the relevant blocklist.
Diferenças principais
252 is a 2xx Positive Completion response, while 554 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 554: The mail transaction has failed. This is a catch-all permanent error that can occur at any point during the SMTP session, including as a rejection greeting when the server refuses all connections from
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 554 when when the entire mail transaction is rejected — often due to spam filtering, blacklisted IP addresses, malformed messages, or policy violations detected during the DATA phase.
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 554 (Transaction Failed): Check your IP against DNS blacklists (DNSBL) and verify your SPF, DKIM, and DMARC records. Review the full error message for specific rejection reasons. If blacklisted, request delisting from the relevant blocklist.