Just to clarify, you are in fact using Two-Step Authentication with G-Suite and an application-specific password?
Try this: http://www.google.com/accounts/DisplayUnlockCaptcha
In your G-Suite Settings, have you allowed the relay to be used with SMTP Auth (as opposed to IP address auth?)
Also, try using TLS on port 587 instead of SSL on 465. G-Suite has a setting to force TLS on relays, that could have been enabled.
I have already set up all steps above, but I also get the similar error. I have tried using TLS on port 587 but it also has the similar error.
Any thing wrong here?
Gmail (particularly its organisational twin, G-Suite) is picky when it comes to its SMTP relays, specifically when it comes to using the LOGIN commands as opposed to XOAUTH2. A quick Google of the error message returns a plethora of users with the identical issue, many of them using PHPMailer.
Essentially, it thinks the connection is suspicious. And, they're probably not wrong. VPS + PHPMailer don't make for a great combination spam-detection wise. I'd flag it too.
According to the unlock page (which I just checked), you should do the unlock and then immediately attempt to authenticate.
I don't really consider Gmail, even G-Suite, a good tool for transactional mail. It's not really intended for it. At best, the G-Suite SMTP relay is a feature implemented so that universities and companies could keep their photocopiers emailing scans to staff after an Exchange migration...
Options:
1. Create another application-specific password, try the unlock again and immediately attempt to authenticate with correct settings (use TLS on port 587).
2. Use IP based authentication in G-Suite settings and supply your VPS' IP address.
3. Look into a better transactional email provider (such as Amazon SES or Sendgrid), or, run your own email server for notification emails.
and I have tried all the g suite retransmission configuration combinations, without success:
The other option of mounting an email server, where can I document?
