File Transfer Protocol: FTP was designed to move files between two computers on a TCP/IP network. IIS supports FTP through Windows Sockets. FTP uses TCP as its transport protocol for all communication and data exchanges between the client and the server. However, IIS communicates with Windows Sockets and then Windows Sockets interfaces with TCP.

Simple Mail Transfer Protocol (SMTP): SMTP is used to exchange mail on a TCP/IP network. Microsoft SMTP uses TCP as the transport protocol for all exchanges between the mail client and server.

Network News Transfer Protocol (NNTP): NNTP is used to read messages posted in newsgroups on the Internet. NNTP uses TCP as its transport protocol for all exchanges between the news client and server.
Connectors appear mostly in the form of extensions in IIS. A connector is an Internet Server Application Programming Interface dynamic link library (ISAPI DLL) that acts as a communications pipe between IIS and a service. The following connectors are supported by IIS:

Microsoft BackOffice connectors: These include:

Microsoft Exchange Server/Web Connector: Supports public folder integration with IIS

ODBC connector Allows communication with any ODBC compliant database engine.

Common Gateway Interface (CGI): Developed for UNIX based systems to extend web server software. IIS supports CGI applications for backward compatibility.

ISAPI filters: Used to pre-process packets before they enter or leave the IIS process. These filters give added flexibility to the IIS architecture. Secure Socket Layers (SSL) is one example of an ISAPI filter.

Active Server Pages: Provides an open scripting system for dynamic creation of Web content.