550 Please turn on SMTP Authentication in your mail client

Message not delivered

There was a problem delivering your message to vicky@stellarmanagement.co.uk. See the technical details below.

The response from the remote server was:

550 Please turn on SMTP Authentication in your mail client. mail-qk0-f172.google.com [209.85.220.172]:34817 is not permitted to relay through this server without authentication.

Final-Recipient: rfc822; vicky@stellarmanagement.co.uk
Action: failed
Status: 5.0.0
Remote-MTA: dns; stellarmanagement.co.uk. (198.252.100.186, the server for the
domain stellarmanagement.co.uk.)
Diagnostic-Code: smtp; 550-Please turn on SMTP Authentication in your mail client.
550-mail-qk0-f172.google.com [209.85.220.172]:34817 is not permitted to relay
550 through this server without authentication.
Last-Attempt-Date: Tue, 24 Jan 2017 16:24:46 -0800 (PST)