Sender email address for automated emails and rules is by default the same email address that is configured for the Bookinglayer account. This email address can be changed by sending a request for support.
Currently it is not possible to set different sender email addresses for separate rules or automated emails.
In case you want to change the domain part of the email address, please check your DNS settings in order to prevent that the emails go to spam folder. For further information about DNS settings , please see this article.