Sending a mail using the command prompt or terminal is possible with a Telnet client.
telnet mail.server.com 25
Press Enter
mail from:<me@mydomain.com>
Press Enter
rcpt to:<someone@else.com>
Press Enter
data
Press Enter
Subject: Some cool subject
Press Enter
This is the body of the email, and you can type your message here
Press Enter
. Enter
Be sure to have “. Enter” (note the space after the .)