php – Mails don’t send on live server but on localhost they work using PHPMailer

I am having a really weird issue which I can’t manage to fix.

The thing is, we had a website hosted in a VPS using Apache, everything was working well. We decided to change the VPS, and I re-installed everything and configured everything exactly like I did on first one.

My problem now is that I have a user registration form that send an activation link, but for some reason it stopped to work on live server.

I am using:

Here is my code:

        //Require PHPMailer class     
        require APP . 'libs/PHPMailer/Exception.php';      
        require APP . 'libs/PHPMailer/PHPMailer.php';
        require APP . 'libs/PHPMailer/SMTP.php';
        $mail = new PHPMailerPHPMailerPHPMailer();
        $mail->Host = '';
        $mail->SMTPAuth = true;
        $mail->Username = 'user'; // Sendinblue Username
        $mail->Password = 'pass'; // Sendinblue Password
        $mail->SMTPSecure = 'tls';
        $mail->Port = 587;

        $mail->setFrom('', 'Example');

        $mail->Subject = 'Example | Account Verification';
        $mailContent = '            
        Thanks for Joining Example! Please activate your account by clicking on the link below.<br/>

        <a href="'.$email.'&hash='.$hash.'">CLICK HERE</a><br/>
        If you did not sign up for an account please disregard this email.

        $mail->Body = $mailContent;

Do I need to open the port 587 on my VPS? I don’t remember doing this before in the old VPS.