Order form that sends email to admin when order submitted from website

Hello, I have a PHP script on my website that sends order form details submitted from website to my email address using the hosting provider's email server and then redirects the visitor to Paypal. I received complains from my hosting provider regarding SPAM (massive emails being sent through my order form). I need you to secure the PHP code of the order form so I can receive the order form by email ** hacking proof please ** Otherwise my hosting will suspend my account. It's a basic order form that redirects to Paypal after sending an email. Bid on this project if you think you can code the send mail feature it securely. Thanks