Not saying there isn't a bug, but did you follow through the troubleshooting link in the error message to see if there was something you could do differently to possibly either get it to work, or get a different error code?
https://support.google.com/mail/answer/78754
yes I did, according to the error message generated by google this really is an authentication error.
Funny enough, later on the day I have received a "blocked login attempt" notification from Google on my personal email, apparently the logon attempt was blocked despite the proper password/account combination. Looks like the way unraid logs in via SMTP doesn't hold up to the security standards google requires:
Sign-in attempt details
Date & Time: Monday, 5 January 2015 01:13:10 o'clock UTC
Location: ************** Canada
If this wasn't you
Please review your Account Activity page at https://security.google.com/settings/security/activity to see if anything looks suspicious. Whoever tried to sign in to your account knows your password; we recommend that you change it right away.
If this was you
You can switch to an app made by Google such as Gmail to access your account (recommended) or change your settings at https://www.google.com/settings/security/lesssecureapps so that your account is no longer protected by modern security standards.
To learn more, see https://support.google.com/accounts/answer/6010255.
Yours sincerely,
The Google Accounts team