Definations:
intranet -a computer network with restricted access, as within a company, that uses software and protocols developed for the Internet.

internet -a vast computer network linking smaller computer networks worldwide (usually prec. by the).

the Internet -The Internet includes commercial, educational, governmental, and other networks, all of which use the same set of communications protocols.

e-mail -a system for sending messages from one individual to another via telecommunications links between computers or terminals.