After a recent windows update, KB4011196 (OL 2010) or KB4011178 (OL 2013), the add-in appears to no longer work when clicking on the Netmail button in Outlook. These two Microsoft patches essentially prevent Outlook from displaying web pages in folders. You can read about this Security Update here:
Please note that only certain installations of Outlook can have this security update applied. Meaning, not all flavors of 2010, 2013 or 2016 can have this security update applied so be aware of that for your environments. The details and requirements to be eligible for this update can be found on the respective support pages:
Outlook 2010: https://support.microsoft.com/en-us/help/4011196/descriptionofthesecurityupdateforoutlook2010october10-2017
Outlook 2013: https://support.microsoft.com/en-us/help/4011178/descriptionofthesecurityupdateforoutlook2013october10-2017
Outlook 2016: https://support.microsoft.com/en-us/help/4011162/description-of-the-security-update-for-outlook-2016-october-10-
There are two options to maintain the Add-in functionality:
Modify the registry with the following key to allow the add-in to work normally as before, without needing to update your add-in.
Install the updated Outlook add-in which will enable the new 'Open in a new window' within outlook option. You then need to change your config.xml to disable the option of 'Open in Outlook'. The option of <Menu>new window</Menu> should be applied see below for config change:
can be "embedded" "new window" "both" or "hidden"
"embedded" will bring a button to open Netmail Archive inside the outlook window
"new window" will bring a button to open Netmail Archive in a new window.
"both" will bring both of the buttons mentionned above, with "(new window)" added on the
caption of the 2nd button to differentiate both of them
"hidden" will hide the menu completely
default value when not specified is "both"
IMPORTANT NOTE: if ArchiveFolderBehavior is set to "new window" then the only acceptable
Menu configuration options are "new window" and "hidden".