If there are other MX entries with lower priority (ex: 0 or 5), emails will not be delivered to Zoho Mail. Ensure that you have deleted all other MX records related to your previous email provider. Ensure that you have turned off 'Local email delivery' in the web host and DNS host ...
The main downside with the MDM policy is that my employer has disabled iCloud Sync, which renders useless so many of the apps I use on my Mac and iPad. So, my iPhone is not a great productivity device in my workflow, and is mostly used for iMessage, email, calendaring, and podcast ...