The response was:
553 Relaying disallowed

Reporting-MTA: dns; googlemail.com
Received-From-MTA: dns; robert.gabriel.balas@gmail.com
Arrival-Date: Mon, 12 Feb 2018 11:14:59 -0800 (PST)
X-Original-Message-ID: <0BCD66D8-2AB5-476C-A525-2ACECF175D94@gmail.com>

Final-Recipient: rfc822; robert@synapsics.io
Action: failed
Status: 5.0.0
Remote-MTA: dns; mx.zoho.com. (204.141.32.121, the server for the domain synapsics.io.)
Diagnostic-Code: smtp; 553 Relaying disallowed
Last-Attempt-Date: Mon, 12 Feb 2018 11:15:01 -0800 (PST)

From: Robert Gabriel Balas <robert.gabriel.balas@gmail.com>
Subject: Re: Test email
Date: 12 February 2018 at 21:14:58 EET
To: Robert Balas <robert@synapsics.io>