This guide was posted by Arco in forum.
As for the Send Email option in the menu Parameters (component) there simply is no "Use Global" value available, that's why the value of email must be set in Parameters (component).
Go to the Components - Phoca Guestbook - Control panel. Click Parameters and scroll down to Send Email parameter. Select the user and save your settings.
Go to the Menu Manager and edit the menu option you have attached your guestbook to (this is the menu option showing on your live website). On the right hand side you can change Parameters (Component). At the bottom you'll find Send Email parameter. This field must also be set to the correct value (i.e. the user you want to receive the e-mail messages). Save the menu option and you're ready to receive e-mails.