1) Start portal
2) Configure the portal to send emails
3) Set the checkInterval of the Asset Publisher to 1 (Control Panel -> Configuration -> System Settings -> Asset -> Asset Publisher)
4) Add a vocabulary and a category to it
5) Put an Asset Publisher to a page and open it's configuration and set:
a) enable email subscription
b) Set filter: contains any of the following categories: [the previously created category]
6) Subscribe to the Asset Publisher
7) Create a new user with the permissions for the category and to create web contents
8) Login with the new user and create a web content categorized with the category created earlier.
Result: The content appears in the Asset Publisher. After an hour an email notification should arrive for the first user but it doesn't.