I am facing this problem since 11/03/2017 until now:
I can't really find a working solution to this since the error is referring to G Suite account while I am using free Gmail account. I cannot setup and send any email directly from my server since I have no static IP and my ISP is blocking port 25 (outgoing).
I do not find gmail info useful so far as they are all now referring to G Suite. Even using G Suite, it still failed though that may be my failure to set properly..
If anybody found any forum/site discussing a how to/solution to this, do link me to it as so far I haven't found one.
I resolved this by removing old settings and configure a new SMTP Relay in my G Suite account.
To note, Gmail SMTP Relay as per my new reading is only available to G Suite account, so no more relay for non account holder a.k.a. free gmail account..
Sorry to bother you guys, but I thought somebody may have some interest on this..