Email delivery problems can often be difficult to troubleshoot, as there are many points along the way where a message could be delayed, rejected, or even silently dropped without the sender ever knowing a problem occurred. 

Account owners have access to their message logs to assist in troubleshooting deliver issues. https://support.duocircle.com/solution/articles/5000699696-viewing-your-domain-message-log-files

Your Email server or Client logs should show what error is occurring; if not, you can contact our support team for further help and make sure to include the full headers of any delayed or rejected Emails (including timestamps and Received: entries) where available, and describe the timeframe of the problem to the nearest hour with timezone.

• Make sure your Email client, or server, is configured to use the following settings:
  

  Outgoing SMTP Server:	outbound.mailhop.org
  SMTP Port:	25 (default), 2525, or 10025
  SMTPS (SSL/TLS):	465 (default) or 10465
  Username:	Your Username
  Password:	Your Password
  Authentication Type:	Basic (“Auth”, “Login”, “Password”)
  Use SSL/Encryption:	Yes (recommended)

• If you use SPF records, make sure to add “include:outbound.mailhop.org” to your record.