188.8.131.52 SMTP_AUTH_NTLM_BLOB_Response Message
The SMTP_AUTH_NTLM_BLOB_Response message is defined as follows. This message is partially defined in [RFC2554] section 4 as a "server challenge response". The 334 status code indicates ongoing authentication and indicates that the <base64-encoded-NTLM-message> is to be processed by the authentication subsystem.
Note that status code 334 is also returned by the SMTP_NTLM_Supported_Response message.