Re-Enabling ND Mail
If you encounter an issue where ND Mail gives you a message that there was a plug-in disabled, this is how to re-enable it
Go to the File menu in the top left, look down and find the 'Slow and Disabled COM Add-ins' icon, it should be highlighted in yellow, like so,

Click the Icon and this menu below should appear.

Expand the options for each Add-in you have in your Outlook to check which Add-ins are still enabled, and which have been disabled. Click the button for 'Always enable this add-in', then click Apply.

When finished, close out of the pop up windows, then restart Outlook.