Office Add-in
The Office add-in can be distributed to users fairly easily, since no installation on the users device is required. In theory (if enabled) each user can just click on “Get Add-ins” in Outlook and install the add-in from there.
You can learn more about the detailed steps here: How-To: Installation Office add-in.
It’s also possible to deploy the Office add-in centrally via Office 365 or Microsoft Exchange, which is explained in detail in the following articles.