Email Spoofing, sending e-mail from someone's account without prior permission.

Hacking has been notorious word for most of us, yup it is a bad thing when it's unethical. There are various forms of hacking, spoofing is one of those forms and Email Spoofing a further offshoot to this plant. Email spoofing is very easy, making an email spoofer is far more easier, just google " making email spoofer with php"
and you shall get the code. Or just google "how to send email through php" and you will get the code, just in place of FROM: variable fill any email adress you want to spoof and that's all, the thing is done. So there are many email spoofers available on internet, the most working and the most hassle free email spoofer is EMKEI'S FAKE MAILER  at www.emkei.cz 
  Warning:  
You can have fun around BUT don't ever try to harm someone with these fake mailers, sending a spoofed email is a CRIME and you can be caught under legal obligations if you try to do so. I know php, so i can make an email spoofer in no time, but i am also a cyber laws aware citizen so i know what problem may i get into if i try such a mischief even for just fun. here's the excerpt from a cyber defense website regarding email spoofing
"Email spoofing is the forgery of an e-mail header in a manner that the message appears to have originated from somewhere other than the actual source.   Email Spoofing is a serious Internet Crime. Allegations of creating a false email header,  email header forgery, or sending a spoofed email are serious cyber crimes accusations requiring the expertise of a computer crime defense attorney.

Email spoofing accusations fall under Email SPAM laws.  A spoofed may appear to be from a legitimate source asking for personal information, passwords, credit card numbers, and other personal information.

Email spoofing is a serious criminal accusation.  Potential penalties for Email spoofing include imprisonment and forfeiture of assets.   Our attorneys are experts in cybercrime defense and in protecting your rights and assets against accusations of criminal email spoofing."
So just have fun but don't you dare  to harm someone with forged emails , you may get into big trouble.