Sometimes, add-ins do not fully load into Outlook, preventing them from being visible (or from working properly). You can tell this is the problem because when you look at the list of add-ins you might see something similar to this:
If so, follow these instructions:
1) Exit Outlook.
2) Download the Office PIAs.
3) Once it is downloaded, right click on the setup file and choose to Run as Administrator.
It is important to run it as an administrator otherwise the necessary files will not go to the correct locations.
4) Once the setup finishes, restart Outlook.
The add-in should now be visible. If not, please contact firstname.lastname@example.org for further help.