This is most commonly due to the default mail program being Mail, not Outlook.
To change this:
Open your Windows Explorer and type in Default Apps.default
Click the Default apps app.
Find the Email option, click Mail. A list of other apps appears.
Click Outlook. This is automatically saved on Windows 10.
To close the window, in the top right, click the X. This should now connect Dimensions to your Outlook and allow the emails to be sent.