External Storage Update notification

Hello. I’m a newbie here, so sorry if I will ask simple things.
The question is about external storage. After a file is added to the FTPS server, that is connected to NextCloud via “External Storage” app, users do not get an e-mail notification about new file creation. I had tried to mark FTPS folder as “Favorite” and get notification about “Favorite” folder changes, but it also did not help. Users still get an e-mail only when those file changes were made by themselves.
Is there some option, how to resolve this problem? The goal is to make system, when external users upload files on FTPS and our users got notification from Nextcloud.