Internet Protocol i.e IP addresses are unique and used for digital data communication for internet. Any mailing system or website technology works on the same principle of digital communication.
Every computer connected to Network have its unique IP address.
When Person A sends an email to person B, The mail is assigned with the header which contains the IP’s of sender and Reciver so that mail can go to the same person B and not to some one else.
Now in a private network for security reasons limited mails are accpeted from reserved IP’s.
In Simple word only internal communication can be worked. Person from outside can’t send mail in that network.
So if attacker wants send the mail inside, He will spoof the IP.
He first will sniffs the data packets in the internal communication adn steal some internal email.
Then he will perform changing in header of the mail. he will change content of the mail and send this mail to network again.
System cant provide security against this because it have internal fake IP.
This is how fake IP is created and attack of spoofing is done.
Thank You all For Reading.