Add-in Express Regions offer many features that can be implemented into existing VSTO Outlook COM Add-in projects: 

• Add regions to practically all Outlook windows
• Create regions for the main Outlook (Explorer) window (up to 17 different areas are supported) or all Outlook item (Inspector) windows
• Multiple regions in the same location are "shared." In other words, they are stacked on top of each other and can be easily switched between by the user
• Regions can be hidden and minimized
• Regions can be dragged and docked into all supported areas that developers allow the users to move them to
• Regions are supported for all versions - from Microsoft Outlook 2003 to Microsoft Outlook 2019

Regions for your existing VSTO projects
This solution effectively allows you to continue designing your Outlook solutions using Visual Studio Tools for Office in Visual Studio. In other words, even if you have an Outlook Add-in project developed with VSTO, you can install Add-in Express Regions and immediately start taking advantage of the powerful Advanced Outlook View and Form Regions technology.