This code is insecure, don’t use it!

[JuliusPC]

Your code contains several security flaws that can and will bite newbies copying the code on their servers.

• you omit htmlspecialchars → XSS
• the form is not protected against Cross Site Request Forgery
• user input is pasted unchecked in the mail’s headers → an attacker could easily send email to other adresses
• there are libraries for sending email: PHPMailer, SwiftMailer
  There is no reason for implementing such thing by yourself.