To send an email with telnet from Linux you only need an open terminal and telnet. Then it is simply a matter of opening a connection to your server and sending it some commands. It is the same commands that your GUI mail client will be doing.
Send An Email With Telnet
The following is how to read your emails. When sending emails you need to start the data part with a subject line as show in the box below.
Subject: Your subject
This must be followed by a blank line. The remaining text until the first full stop at the start of a new line will be the message body.
telnet mailserver.dragon.lab smtp
Connected to mailserver.dragon.lab.
Escape character is ‘^]’.
220 mailserver.dragon.lab ESMTP Postfix
MAIL FROM: firstname.lastname@example.org
250 2.1.0 Ok
RCPT TO: email@example.com
250 2.1.5 Ok
354 End data with <CR><LF>.<CR><LF>
Subject: Your first test email with POP3
This is your first test email.
250 2.0.0 Ok: queued as 57FB240C20
221 2.0.0 Bye
Connection closed by foreign host.