Outlook add-in doesn't install with message about certificate or location not trusted

Some users have reported that when attempting to download and install the Soup Mail Outlook Add-in, installation is unsuccessful and a message is shown relating to the certificate or location not being trusted. The message looks something like this:

The resolution is to add the download location of our add-in to your trusted sites, as follows:

1. From the Windows (Cortana) search box, type "Internet Options" and select the Internet options control panel result to launch the dialog.
2. Click on the "Security" tab, then on "Trusted Sites"
3. Now click on the "Sites" button
4. Add the sites http://addin.soupmail.com https://addin.soupmail.com to the list by entering them into the field at the top and clicking "Add" (you may need to un-check "require server verification (https:) for all sites in this zone)
5. Close the dialogs (and Internet Explorer)
6. You should now be able to re-run the launcher that you downloaded and successfully install the add-in

If these steps don't work and you still get trust errors on installation, you may need to update some registry settings instead, as follows. You may need an administrator of your computer to assist with this if you don't have permission to edit the registry.

1. Launch the Registry editor (Regedit) from search.
2. Navigate to \HKLM\SOFTWARE\MICROSOFT\.NETFramework\Security\TrustManager\PromptingLevel
3. Change the values of the registry entries here as follows:
   • Internet = AuthenticodeRequired
   • LocalIntranet = Enabled
   • MyComputer = Enabled
   • TrustedSites = Enabled
   • UntrustedSites = Disabled
4. You should now be able to re-run the launcher that you downloaded and successfully install the add-in