In principle, setting up the custom field of the type External file works with all servers that comply with the WebDAV standard (see External files).
We know that customers have successfully used, for example, the following online storage systems in combination with portatour®:
If you run servers in your company yourself: Both the Apache web server and Microsoft IIS support the WebDAV protocol. Make sure that the portatour® server my.portatour.net can access your WebDAV server over the Internet.