If you launched it from Google Cloud Launcher, then it is a Bitnami image.
Quoting StackOverflow answer:
Google Cloud Platform doesn’t allow SMTP traffic through default ports: 25, 465, 587. You can check Google Cloud Documentation to configure a third-party mail provider like Sendgrid, Mailgun or Mailjet. If you use Google Apps you can also use it to send email through 465 or 587 ports.
Another alternative could be that you use your own email server on a custom port or using a VPN to bypass that port restriction.
You can find more info on Bitnami Wiki page for Google Cloud Platform
If you find more issues with the Discourse Bitnami image or installer, you can post them in our “Discourse powered” community forum at https://community.bitnami.com 
Regards,
Jorge
Disclaimer: I work at Bitnami