How configure my web server with my mail serveer

My problem is the following, I have an email server with postfix and a web server in different droplets, and my application uses phpmailer to communicate with the email server, but I have no idea how to get it work with my email server, and I have other problem and is that at beginning I used gmail as email server and my domain is configured with Gmail MX in Godaddy and I don´t know how to change them.

Phpmailer Source public function __construct() { { $this->mail = new PHPMailer(); $this->mail->IsSendMail(); $this->mail->Host = ‘xxxx.xxxx.xxxx.xxx’;//Private IP $this->mail->Port = 25; $this->mail->Username = ‘root’; $this->mail->Password = ‘’; $this->mail->SetFrom(‘user’, ‘My Page’); }