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 RFC 2119. Sections 1.5 and 1.9 are also normative but cannot contain those terms. All other sections and examples in this specification are informative.