In order to send a fake mail we would interact manually with a SMTP or Simple Mail Transfer Protocol server which usually runs on port 25 and is used for sending mails. So, telnet to port 25 of an SMTP server by clicking Start > Run and type "telnet server_address.com 25" (without quotes) and wait for the Daemon banner. A Daemon banner is nothing but a piece of welcome message containing name and version of server, date, day & time etc. which is displayed when we connect to any service. Now you would get something like following:

220-server_address.com ESMTP Exim 3.36 #1 Tue, 03 Dec 2002 23:34:45 -0500

Now you need to give the following commands to the server to send a fake mail. The text below written in bold is the commands that you need to send and the text in normal is the server resonse against your command and line starting with '#' are just the comments so that you can understand everything easily.

HELO microsoft.com
250 server_address.com Helo microsoft.com [***.***.***.***]
# This command is used to introduce yourself to the server. I'll recommend you using the same domain that you are using in sender's email address to make the mail look more original. The text in brackets censored by * is my IP address and the text "250" in the beggining of the line is server's message code which is different for all types of server response.
MAIL FROM:billgates@microsoft.com
250 <billgates@microsoft.com> is syntactically correct
RCPT TO:victim@address.com
250 <victim@address.com> is syntactically correct
DATA
#This command is used to enter the mail contents.
354 Enter message, ending with "." on a line by itself
#You can define your custom headers below.
Date: Tue, 03 Dec 2002 23:34:45 -0500
From: billgates@microsoft.com (Bill Gates)
To: victim@address.com
Subject: Subject Goes Here
Reply-To: billgates@microsoft.com
Hi,
This is my first fake mail to you ;) :P.
.
# Use `.` to end your message in a new line.
250 OK id=18JRPd-0006oQ-00
# Confirmation from server along with message id.
QUIT