SMTP code 252 is returned in response to a VRFY or RCPT TO command when the server cannot confirm whether the mailbox exists but will accept the message for delivery anyway. This is a deliberate security measure — many servers disable VRFY to prevent address harvesting by spammers, and some return 252 instead of a definitive 250 or 550 for RCPT TO to avoid revealing which addresses are valid. The message will be accepted and the server will attempt delivery, but the sender will not know in advance whether the recipient is valid.
Most modern mail servers disable or restrict the VRFY command to prevent spammers from probing for valid email addresses. Instead of returning 250 (valid) or 550 (invalid), they return 252 as a non-committal response.
Some mail servers (especially those using catch-all configurations or backup MX relays) accept all RCPT TO addresses with 252, deferring recipient validation until after the DATA phase. Invalid addresses result in bounce messages later.
The mail server needs to query an external directory (LDAP, Active Directory) to verify the recipient, but the directory is temporarily unreachable. Rather than reject the message, it accepts with 252 and will attempt delivery.
Instead of using VRFY, send a test message through the full SMTP flow. If RCPT TO returns 250, the address is verified. If it returns 252, the server is intentionally not confirming the address.
openssl s_client -connect mail.example.com:25 -starttls smtp
Verify that the MX records point to the correct mail server. If you are getting 252 from a backup MX, it may be accepting all addresses and relaying them to the primary.
dig MX recipient-domain.com +shortCheck DNS Records
After sending to an address that returned 252, check your inbox for NDR (Non-Delivery Report) bounce messages. The 252 at SMTP time does not guarantee delivery — the actual recipient validation may happen later.
The SMTP command was successfully processed. Used for EHLO responses, MAIL FROM, RCPT TO, and DATA completion.
The recipient's mailbox does not exist, or the server has permanently rejected the message due to policy.
The email address syntax is invalid or the mailbox name violates server naming rules.