What to do if ur net identity is stolen and somebody sends a malicious e-mail which is highly punishable, you will be lodged in a jail. Remember what happened in Shivaji Case, an innocent was lodged in jail for many months. So how to prove that the message is not sent by your computer, I got a useful bit of information in a paper..........
Go to run
Type cmd and open it
In that type ipconfig/all
In that there will be something called physical address which is a 12 digit number or words two by two separated by a dash. If somebody hacks your mail account and sent a mail your IP address will be there on it but this unique MAC media access control or physical address will not be copied.