1.4 Relationship to Other Protocols
The NT LAN Manager (NTLM) Authentication: Simple Mail Transfer Protocol (SMTP) Extension uses the SMTP-AUTH extension mechanism, as specified in [RFC2554], and is an embedded protocol. Unlike stand-alone application protocols, such as Telnet or Hypertext Transfer Protocol (HTTP), NTLM Authentication: SMTP Extension packets are embedded in Simple Mail Transfer Protocol (SMTP) commands and server responses.
SMTP specifies only the sequence in which an SMTP server and an SMTP client exchange NTLM messages to successfully authenticate the client to the server. It does not specify how the client obtains NTLM messages from the local NTLM software or how the SMTP server processes NTLM messages. The SMTP client and SMTP server implementations depend on the availability of an implementation of the NTLM Authentication Protocol (as specified in [MS-NLMP]) to obtain and process NTLM messages and on the availability of the base64 encoding and decoding mechanisms (as specified in [RFC1521]) to encode and decode the NTLM messages embedded in SMTP packets.