You have enabled SMTP authentication for the IP range that the user is connecting from, but the user has not configured his client to use SMTP authentication. Either configure your email client to use SMTP authentication.This setting is normally found in the account settings in your email client. The first solution is recommended since it reduces the risk that anyone will send spam through your server.By default, h Mail Server never requires SMTP authentication for deliveries to local accounts, since that would prevent other e-mail servers to deliver email to your installation.
Technical details of permanent failure: Google tried to deliver your message, but it was rejected by the recipient domain.
We recommend contacting the other email provider for further information about the cause of this error.
The error that the other server returned was: 530 530 5.7.1 Client was not authenticated (state 13).
Generally this is because the eternal mailer (Gmail in this case) attempted to send email anonymously, when Exchange was expecting an authentication.
By default, h Mail Server does not require SMTP authentication for connections coming from localhost / 127.0.0.1.
For connections coming from other hosts, SMTP authentication is required for deliveries to external recipients.
If a SMTP client tries to use the TURN command h Mail Server responds with this error code.
h Mail Server does not include support for the TURN verb.
A client should never do this, but incorrectly configured clients could cause this problem.