[Plugin: easyReservations] Email problem

Hello,
I use your plugin, but I do not understand how the email function works. Indeed, when a guest books a room, an e-mail is sent, isn’t it ? But how does it work ? How can I send automatically an email ( from [email protected]) to a guest ([email protected]), if I do not fill my password email ?

Best regards

http://ww.wp.xz.cn/extend/plugins/easyreservations/