With each new post an email is sent to every registered User in the Database. The email can be text or HTML.
Just copy the post-notification folder into your plugins folder. If you have the old post_notification (underline) it's probably the best to just rename it.
Activate the plugin, configure it carefully (options->Post Notification) and off you go. For support please see the Forum: http://pn.xn--strbe-mva.de/ An please report problems. I can only fix stuff if I know that they are broken.
Unfortunately a lot of hosters have set up their php-mail settings incorrectly. If you experience any problems with mails not or wrongly sent please install WP MAIL SMTP.
Auto update It might be, that the auto update deletes all your self-created profiles. I haven't tested auto update and feedback is welcome.
You might get errors, because old translations are not working. You can delete those dirs. (ru_RU, etc)
You have to update your old templates: