3.1.5.2 Receiving a POP3_AUTH_NTLM_Fail_Response Message
Expected state: sent_authentication_request
On receiving this message while in this state, a client MUST abort the NTLM authentication attempt.
Expected state: inside_authentication
On receiving this message while in this state, the POP3 client MUST change its internal state to completed_authentication and consider that the authentication has failed. The client can then take any action it considers appropriate; this document does not mandate any specific course of action.