links to intranet ressources won't work

Hello!

In our organisation we used to work with both links to URLs and links to folder and files in our Intranet in Outlook-Emails.

Links to the WWW are still working fine.
But links to Folders and Files don't work anymore.
Why is that? How can I fix this?

We just klicked on the Link and the File/Folder opened.
But now we need to copy the Link and paste it into Windows Explorer. Thats kind of elaborate.

We use:
Microsoft Office Professional Plus 2016
Windows 10
Outlook 2016 (16.0.5408.1000) MSO (16.0.5404.1000) 32-Bit

Thanks!