I am trying to install a custom Outlook add-in for the OWA, however when I attempt to install the XML manifest file I receive an error stating that the app isn't supported by the current version of Exchange Server.
There is not an XML file in the application folder by default, so in order to comply with the request for an XML, I changed the file extension of the Manifest file from .manifest to .XML.
The OWA custom add-in installer does not seem to recognize this as the correct file.
Which file should I use, or what am I doing wrong?
OWA can't run VSTO add-ins. Instead, you need to create a Mail App (so-called Outlook Add-in). See Get Started with Outlook add-ins for Office 365 for more information.