We have built an email filing application that is an Outlook web add-in which files emails from user's inboxes to wherever they would like to organise them; typically as MSG or EML files on external storage.
One customer has started to use 'Groups' in Outlook and has found that he can't use our application to file emails that are in these types of folders.
I hoping that someone has some experience of this and can provide some guidance that I can pass on to the developers.
Web addins are activated in context of mailboxes, and since Groups are not mailboxes, no web addins can be pinned or used against group messages/folders. You can still access messages like that though Graph in your web addin, it is just your addin cannot be pinned or invoked in a context of a such message.
Outlook COM addins (VSTO if you are using .Net) can access such messages just fine - Explorer.CurrentFolder / Explorer.Selection etc., work as expected when group folder / message are selected.