Add-ins for Outlook in Exchange Online
Add-ins for Outlook are applications that extend the usefulness of Outlook clients by adding information or tools that your users can use without having to leave Outlook. Add-ins are built by third-party developers and can be installed either from a file or URL or from the Office Store. By default, all users can install add-ins. Exchange Online admins can control whether users can install add-ins for Office.
For information about add-ins for Outlook from an end-user perspective, check out the Help topic Installed add-ins at Office.com. That topic provides an overview of the add-ins and also shows you some of the add-ins for Outlook that might be installed by default.
Office Store add-ins and custom add-ins
Outlook clients supports a variety of add-ins that are available through the Office Store. Outlook also supports custom add-ins that you can create and distribute to users in your organization.
Access to the Office Store isn't supported for mailboxes or organizations in specific regions. If you don't see Add from the Office Store as an option in the Exchange admin center under Organization > Add-ins > New , you may be able to install an add-in for Outlook from a URL or file location. For more information, contact your service provider.
Some add-ins for Outlook are installed by default. Default add-ins for Outlook only activate on English language content. For example, German postal addresses in the message body won't activate the Bing Maps add-in.
Add-in access and installation
By default, all users can install and remove add-ins. Exchange Online admins have a number of controls available for managing add-ins and users' access to them. Admins can disable users from installing add-ins that are not downloaded from the Office Store (instead they are "side loaded" from a file or URL). Admins can also disable users from installing Office Store add-ins, and from installing add-ins on behalf of other users.
To install add-ins for some or all users in your organization, see Manage deployment of Office 365 add-ins in the Office 365 admin center