Chapter 23, “Developing COM Add–Ins for Word and Excel,” examined several issues with building COM add-ins in Visual Basic for Office applications. In particular, the chapter considered several problems with using the default configuration of a COM add-in where mscoree.dll loads the COM add-in:
• mscoree.dll can be disabled, causing all managed COM add-ins to stop loading.
• mscoree.dll cannot be signed, which makes it so your COM add-in cannot be loaded when the Trust All Installed Add–Ins and Templates option is not checked.
• mscoree.dll loads all COM add-ins into the same application domain, which allows COM add-ins to affect one another adversely.
VSTO add-ins for Outlook ...