Manage Addons Office Store - Exchange 2016 OP

You don't need online exchange account. 

You can install add ins for all or select users - https://docs.microsoft.com/en-us/exchange/install-or-remove-outlook-add-ins-2013-help

If you want to prevent users from installing addins then 

• To prevent users from installing Office Store add-ins, remove the My Marketplace role from them.

• To prevent users from loading add-ins from sources other than the Office Store, remove the My Custom Apps role from them.

• To prevent users from installing all add-ins, remove both of the above roles from them.