I used to use Wingate for Windows 95, but it wasn't the best solution. Someone told me about a feature called IP masquerading in Linux. With only one account, the three computers can now access the Internet. All of this software is free, of course. A company would probably not use Linux in the same way I do.
Server software is quite expensive.
Linux comes with sendmail, an SMTP mail server. You can access the server with a POP3 mail program, such as Netscape, Internet Explorer, Eudora, etc. Note that the client computers do not need to run Linux. They can be Macintoshes, or PCs running Windows 3.1 or Windows 95. The most basic use of a server is usually a file server.