This only happens in Outlook for Windows.
There are two installs for ndmail:
1. The Traditional Windows Program
2. The Office 365 Plugin
The Office 365 Plugin allows you to use ndMail on an iphone, an android device, and a Mac.
If you have enabled ndMail for office 365 so you can save emails on your iPhone, it will show up in Outlook as you can see above. You want to avoid using that on your Windows Outlook and just use the lower ndMail Option.
To make this easier for me, I just hid the Office 365 ndMail option.
Step 1: Right Click on a Blank Space on the Outlook Ribbon. Choose Customize the Ribbon
Step 2: Remove the NetDocuments Column