Using restricted Gmail SMTP server with no auth

I’ve setup a Ghost blog for internal use at our company and want to use the no-auth-required GMail SMTP relay service for transactional emails, detailed as option 3 here: Google SMTP Relay service

I’ve tried a bunch of settings but keep getting refused because of server error. Anyone got tips for getting this off the ground?

The pros of using this setup is that it doesn’t rely on any one account for auth, so even if I were to leave this company the blog would still work after my account was removed.
The con is that we can only send transactional emails to GMail/Google Workspace users, which is fine because we’ll only be sending them internally.

Below is the most recent attempt, I’ve tried without the “service” and “auth” tags without luck.

  "mail": {
    "transport": "SMTP",
    "options": {
      "host": "",
      "port": 25,
      "service": "Gmail",
      "auth": {
        "user": "",
        "pass": ""

Latest version of Ghost, 5.44.0
Running on Ubuntu on EC2
Latest Node and MySQL versions