I have developed an STVO add-in for Outlook. This add-in works great on both my personal computers (Office 365) and my company computer (also Office 365).

However, an acquaintance for whom I programmed the add-in (Microsoft Professional Plus 2019) always gets the following error (error message translated into English, it may be slightly different): User-defined functions cannot be used in this application because the certificate used to sign the deployment manifest for XXX or its location is not trusted.

On all other machines I just get a warning that it could be a potential threat, but on the acquaintance's machine the above error message comes up and you can't install it.

What do I need to change so that he can install it too?

CodePudding user response：

Assuming your add-in isn't signed with a trusted certificate but perhaps yours, Outlook doesn't recognize the publisher. For commercial use, it is recommended to sign the code with a "code signin certificate" issued by a trusted authority so that all customer PCs recognize the certificate. Once you have the certificate, follow these simple steps written in the documentation to sign the project How to: Sign Office solutions

I hope I have been helpful

CodePudding user response：

Try to install the certificate before to running the installer - in Windows Explorer, right click on your signed file, Digital Signatures | Details | View Certificate | Install Certificate.