Hello, thx for your suggestions. Indeed, those include every option except the one we need. ; ) Can’t deploy with group policy, have to use MDT. You can see in the MDT instructions you refer to, they mention the command line instruction there, for Acrobat, for example (see below). There must be some syntax for the .msi to do a silent install. Often you can find similar info around the internet from people who have done it before, but in the case of Mattermost, I have found nothing so far.
