550 Error - "Please turn on SMTP Authentication in your mail client"

550 Error - "Please turn on SMTP Authentication in your mail client"

Hello, I can't seem to receive emails and when someone does it bounces back to their email and they receive this as an error:


Message not delivered

There was a problem delivering your message to louis@twointeractive.com. See the technical details below, or try resending in a few minutes.
The response was:

550 Please turn on SMTP Authentication in your mail client. mail-qk0-f173.google.com [209.85.220.173]:36580 is not permitted to relay through this server without authentication.


Final-Recipient: rfc822; louis@twointeractive.com
Action: failed
Status: 5.0.0
Remote-MTA: dns; twointeractive.com. (199.79.62.11, the server for the domain twointeractive.com.)
Diagnostic-Code: smtp; 550-Please turn on SMTP Authentication in your mail client.
 550-mail-qk0-f173.google.com [209.85.220.173]:36580 is not permitted to relay
 550 through this server without authentication.
Last-Attempt-Date: Mon, 15 May 2017 09:50:37 -0700 (PDT)


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I have already updated the MX records properly on my host which is Hostgator. I can send emails but cannot receive. Hoping to have this fixed asap.