We are using ZohoMail to as a our company's email service solution. 

There is a webform on our website which allows users to fill in and submit request. See http://www.yivadigital.com/about#contactus_form.  We have used Zoho Mail's SMTP on the website, but there is no way to send out the notification email from the website. 

Our developer mentioned there is an issue with Zoho Mail raised by other people. See post: https://help.zoho.com/portal/en/community/topic/problem-sending-email-with-smtp-authentication-and-relaying-disallowed-message-28-1-2013 

Please advice what's the best way to solve this.

Thanks,