I have created an Outlook Add-In and created an installer in Advanced Installer. I have the installer signed and the publisher shows up and everything seems ok but after the Add-In has been installed and Outlook is opened this message appears (see attached image).

1. Why does the publisher say "unkown" when it has been signed with a valid code cert? Is there another step I might be missing? When doing the initial installation the publisher shows up correctly. It's only this popup in Outlook afterwards that says "unkown".

2. Is there a way to configure the installation in a way that this message will not popup to the user?

Thanks.

Hello and welcome to our forums,

I'm afraid that this is not an installer issue and therefore I can't fully assist.

However, I have found the following thread where a user seems to have found a solution for this (it's some setting from Outlook itself):

Re: No Trusted Publisher Option for VSTO for Excel

Could you please have a look over that and let me know if it helps?

Best regards,
Catalin

Thank you for the reply. Unfortunately those options that are available in Excel don't exist in Outlook.

Hello,

Upon further investigation, it looks like the solution would be to install the certificate on that machine:

Unknown Publisher still appears on correctly code-signed VSTO addin built with VS2010

Signed VSTO Deployed with ClickOnce Showing "Unknown Publisher"

As we can see from the above StackOverflow threads, this is not an issue with the setup package itself so I'm afraid I can't assist much here.

Hope this helps!

Best regards,
Catalin