The NT LAN Manager (NTLM) Authentication: Simple Mail Transfer Protocol (SMTP) Extension specifies the use of NTLM authentication (as specified in [MS-NLMP]) by the Simple Mail Transfer Protocol (SMTP) to facilitate client authentication to a Windows SMTP server. SMTP specifies a protocol for reliable and efficient transmission of email. A detailed definition of SMTP is specified in [RFC5321] and [RFC5322].
The NT LAN Manager (NTLM) Authentication: Simple Mail Transfer Protocol (SMTP) Extension uses the SMTP-AUTH command (as specified in [RFC2554] section 4) and SMTP response codes to negotiate NTLM authentication and send authentication data.
Sections 1.8, 2, and 3 of this specification are normative and can contain the terms MAY, SHOULD, MUST, MUST NOT, and SHOULD NOT as defined in [RFC2119]. Sections 1.5 and 1.9 are also normative but do not contain those terms. All other sections and examples in this specification are informative.