ColdFusion Relaying with Google Workspace

I'm not experienced with that specific problem, and someone may offer a better answer, but first are you using a username and password in the cf admin mail page? (or in the cfmail username and password attributes?) 

Second, the error could be misleading and there may be other issues. 

For instance, when I have setup my mail client to connect to gmail, I had to tell Gmail to allow "less secure apps". And in another setup I had to create a new and special username and password for that email, for use with such a less secure app. Do you recall doing either of those? Or does anyone else reading this? 

Finally, some problems happen that are fixed with later versions of cf, or later updates to a particular version, or updates to the jvm that Cf is using. What cf version, update, and JVM version are you using? This is shown on the CF admin "settings summary " page.