3.1.5.3 Receiving an SMTP_AUTH_NTLM_BLOB_Response Message

When the client state equals sent_command and on receiving this message, a client MUST change its internal state to received_response, de-encapsulate it to obtain the embedded NTLM message, and then pass it to the NTLM software for processing. The NTLM software then extracts the NTLM CHALLENGE_MESSAGE and produces an NTLM AUTHENTICATE_MESSAGE response. The client MUST then encapsulate the NTLM message, as defined in section 3.1.4.2, send it to the server, and transition to the sent_command state.