I can receive an e-mail with all the modification I make to the folders BUT I can’t have a mail with the modification that OTHER people makes to the folder that my account can see. If I access the web part I can see on the upper part all the modified files but why can’t I receive a daily mail with these information? This will be very useful for the read-only users that doesn’t access every day but that can be invited to access if there is a useful modification of the files they want to follow.
In your personal options, you can configure for what action your are informed per mail (https://docs.nextcloud.com/server/16/user_manual/userpreferences.html). What did you set there?
Since you are receiving mails for other actions, I suppose the e-mail configuration and the cronjobs work fine.