Nodemailer and Hostmonster: Receive 250 OK but unable to send email to external domains

Question

Here's my nodemailer config:

var mailTransporter = nodemailer.createTransport({
  host: "mail.domain.com",
  port: 26,
  auth: {
    user: [email protected],
    pass: RESET_PASSWORD
  },
  secureConnection: true,
  debug: true,
  logger: true
});

I receive a 250 OK response when I send an email, but it is not received by external domains, even spam checkers such as http://isnotspam.com/

However, it is received by users on the same domain ([email protected])

I have no problems sending to external domains when using the cPanel webmail or Thunderbird. I've tried to configure nodemailer to be very similar to Thunderbird, but still no luck.

I've tried different ports supported by Hostmonster such as port 465, same result.