I have just tested the TRIAL edition on my J25 server and everything is working fine. I do get email notifications.
I will try to help you but will then need admin and FTP access to your website. I will send you an email, don't publish any access details on this forum!
The existing postmaster address that you mentioned is just to have a sender address attached to the notification email. The address will be of the format This email address is being protected from spambots. You need JavaScript enabled to view it.

Whenever occurs some modification on the website, which triggers jhacker plugin, I get an error: "The following from address failed: This email address is being protected from spambots. You need JavaScript enabled to view it." (I just filled up with "my-domain", but in fact is my real domain that is showing, and is postmaster too that is showing) and never get the notification in my email.

I've setted up to send notification to email list. I don't know where did start this problem.
I've checked my database, an my email list is save in the plugin configuration.

I noticed that in the jhackerwhatch.php there's an setting to "postmaster@server", but I can't go further alone in this quest.

Can you help me solve this?