The DCOM, RPC, WinSock, and WinInet examples above illustrate an important concept with respect to SSPI:
It does not matter which underlying protocol the distributed application is built on, as long as the application protocol defines security requirements for connection authentication, message integrity, message privacy, and security quality of service, SSPI can be used as the common abstraction layer to obtain these services.
Therefore, other protocols like POP3, LDAP, IRC/MIC, IMAP, and so on. can be implemented using SSPI to take advantage of the integrated security services available in Windows NT.