What is email forging???

Email forging allows an attacker to disguise the source of an email and send it to the victim. Most attackers use this technique to fool the victim into believing that somebody else has send the particular email.
The SMTP protocol makes it extremely easy for an attacker to send forged emails to a remote user.
Typically an attacker carries out email forging by following steps:

1) Start Command Prompt and type the following command-
c:/>telnet smtp.mailserver.com 25 or c:/>telnet mail.domain.com 25
example:- c:/>telnet smtp.gmail.com 25
The above command opens a telnet connection to the specified remote mail server on port-25. Where port-25 is the default SMTP port on which outgoing mail daemon runs.