As admin you can install an add–in for your whole organization so that all users have access to it.
1) Go to the "Admin" page
2) Under "Admin centers" choose "Exchange"
3) Click "add-ins" under "organization"
4) Choose "Add from the Office store" option
5) In the Office store type 'yoxel' in the search box to find Yoxel Mailbox Assistant and then click the 'Add' button on the listing.
6) Once the add-in is added edit its settings to specify its availability