How to send emails from a form on a website via postfix?

Question

PHP

I have a website and it has a submit form. There is a handler (send.php) in the site directory, it should send the form via mail(). Naturally, he doesn't. I configured mail() in php.ini, now it at least responds to messages, but does not send mail, then I installed postfix, it is fully working. Question: how to link php and postfix.
Maybe I searched the Internet badly, or maybe there is an easier way. What options are there and is it possible to implement what I want through postfix?