Pictures and PDF can be viewed very comfortably in the web app. For other attachments, the file must first be downloaded to the mobile device before it can be viewed.
But at that point I’m rather unhappy. The last used directory is always suggested for saving. If you only want to view a file without actually needing it locally, you quickly create a big mess. If you’re not careful every time, the downloaded attachments are distributed all over the device or even the server.
A way out of this would be if Kopano provided the attachment in a special file share where it is visible only to the current user and only as long as the associated mail is displayed and the file is still open in the corresponding application. Then you could open the file without having to download it first and would have no leftovers if you had worked through a few mails with attachments.
This would be possible at least for users working in the same network as the server or connected via VPN. Users without access to the internal network would probably have to live with the problem.
Translated with www.DeepL.com/Translator