When using Hoxhunt button in OWA that is hosted on an on-premise Exchange Server 2019, 2016 or 2013, users may be presented with a dialog asking to trust the mail server where their Outlook Web Access is hosted.
An embedded page at appsforoffice.microsoft.com says
The domain [mail.example.com] is acting as Microsoft Office and can run Office add-ins, which may access your personal data. If you trust the domain to run as Office and access your data, click OK to continue.
To record the response and enable the add-in, you must enable third-party cookies for the domain that's hosting OWA or Office Online Server in the browser settings. To enable this setting, refer to the specific support documentation for the browser.