I'd like to know if it's possible to use PHPMailer to transmit mail via the SMTP relay service. I have written a small plugin to send emails from the WordPress admin dashboard to but I get an error connecting to the relay server with my settings and credentials.

I've not set tls or ssl but left that blank after failing with tls, and I have smtp authentication set to true.

This is my PHPMailer settings info:

$phpmailer->isSMTP();
    $phpmailer->SMTPDebug = 2;
    $phpmailer->debug     = 1;
    $phpmailer->Host       = $host;
    $phpmailer->Port       = $port;
    $phpmailer->SMTPSecure = $smtpsecure;
    $phpmailer->SMTPAuth   = $smtpauth;
    $phpmailer->Username   = $username;
    $phpmailer->Password   = $password;

Is the problem that PHPMailer is not compatible with dynu?