In order to install the Outlook add-in an admin user will need to:
On the Ribbon, click Plugins and then click RDB Store.
Log in to the RDB Store.
Click All in the Left hand side column.
Under the plugin column search for Outlook add-in.
Click Install.
Assign to users who need the plugin.
The options on the plugin page in the store will change. All users who want the plugin will now need to:
On the Ribbon, click Plugins and then click RDB Store.
Click All in the Left hand side column.
Under the plugin column search for Outlook add-in.
Click the relevant add-in depending on the version of outlook they are on.
Restart Outlook.