Before email program like Outlook or Mozilla thunderbird exists, telnet is the program you use to send email. This method is considered old enough and it exist at the beginning of the internet itself.
The items in bold are what you should type.
Start telnet by the following command at your command prompt/shell
telnet inertz.org 25
220-my.internet-webhosting.com ESMTP Exim 4.68 #1 Sun, 24 Feb 2008 11:17:08 +080
220-We do not authorize the use of this system to transport unsolicited,
220 and/or bulk e-mail.
250 my.internet-webhosting.com Hello [184.108.40.206]
mail from: firstname.lastname@example.org
354 Enter message, ending with “.” on a line by itself
This is test.
250 OK id=1JT7R9-00066M-7Z
221 my.internet-webhosting.com closing connection
Connection to host lost.