I get a 550 error when sending email from Gmail to my Zoho hosted email

I get a 550 error when sending email from Gmail to my Zoho hosted email

I set up my email (registered with hostgator) to be hosted on Zoho. Everything waas fine, I sent and receive a few test email and everything was ok. When I sent another email from my Gmail acccount I got the Delivery error 550.

Delivery to the following recipient failed permanently:

     xxxx@mywebsite.com

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain my@website.com by my ip.

The error that the other server returned was:
550-Please turn on SMTP Authentication in your mail client, or login to the
550-IMAP/POP3 server before sending your message.  mail-wg0-f52.google.com
550-[74.125.82.52]:52395 is not permitted to relay through this server without
550 authentication.

Any idea on how to solve this?