Having trouble with emails not sending from zoho mail web client

Having trouble with emails not sending from zoho mail web client

Hi we have been having this problem from a few of our email accounts where they are unable to send the email at first and then if they try to send it multiple times quickly the email appears to send but does not show up in sent. 

The Error is shown below.

Unable to connect SMTP server:smtp.goric.com Reason:Unknown host: