change the way emails are sent from my website - PHP mail function to SMTP - PHPMailer

Hello, I am running a website that is based on the php template engine called smarty. I want that the emails that are send through the website are no longer send thorugh php mail function but through SMTP. I know there are some finished scripts for that like PHPMailer but it need to be integrated in the script the website is running. So for example when a new member registers for an account he should get an email with the activation link but the email should be send through SMTP automatically. If you have further questions, let me know.