Internet Explorer 11 (IE11, Trident) is a legacy web browser but still used by Office add-ins running in Windows Outlook.
Microsoft's own M365 Apps will officially stop supporting Internet Explorer on August 17, 2021. However, while Hoxhunt add-in will continue to work with Internet Explorer even after August 17, 2021, we strongly recommend our customers to upgrade to Microsoft Edge Chromium for optimal performance with Hoxhunt add-in.
Read more: https://techcommunity.microsoft.com/t5/microsoft-365-blog/microsoft-365-apps-say-farewell-to-internet-explorer-11-and/ba-p/1591666
All Windows Office add-ins use Internet Explorer to render HTML content by default. Only if you are running Outlook 2019 in Windows 10 version 1903 or later, Edge will be automatically preferred over IE11. Which browser is used in each scenario, please check this MS article: https://docs.microsoft.com/en-us/office/dev/add-ins/concepts/browsers-used-by-office-web-add-ins
Settings requirements in a nutshell
Protected Mode should be enabled on security zones (Internet, Trusted site and Restricted sites)
Compatibility View should be disabled
Hoxhunt add-in should not be running under Intranet security zone
'Access data sources across domains' should be allowed
Pop-up windows should be allowed