How to troubleshoot a VSTO addin that does not load?
Here’s a bit more detail on RobertG5’s solution (too long for a comment): The problem was that the add-in had been hard disabled by Outlook. As I’ve learned, that’s something different than the “usual” not-loading scenario. The key to realizing this was to notice that the add-in did not show up under Inactive Application Add-Ins, … Read more