You can use Telnet for more than just a virtual terminal, however. We mentioned using telnet to test services that you have configured. Telnet provides a virtual terminal that opens a TCP connection to a specific port. This connection will print whatever text it is sent from the server (in this case, the Telnet server) and will send any data you type into the remote server.
Quite a few services work on this notion of sending their data in plain text form for their protocol. The two main candidates are Hypertext Transfer Protocol (HTTP) and Simple Mail Transport Protocol (SMTP).
To see a rundown of the SMTP protocol, we will log into the mail server on our local machine and will send a test mail (see Listing 15-9).
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