Can I create a smart agent that sends an e-mail to a user when a specific category is updated on the site?
Hay Hadar, While we do not have such a feature built into the product, you can craft one yourself using a bit of coding.
In the answer for Submission Notification we show how you can send an email on a form post. In your case you can use a wix-data afterInsert and afterUpdate hooks to trigger an email to notify a user on a data change.
Another option is to use the same hooks and a service like IFTTT or Zapier to trigger actions (on those services), allowing you to notify users using different means, including email, sms, and many more.
We’ve just added a new article on this subject:
https://support.wix.com/en/article/sending-an-email-on-form-submission