BackOffice>>Preferences>>Email
The email contacts come from the employees you have set-up (BackOffice>>Employess>>Contacts). These contacts are used in your FronOffice contact form and in this section allow you to specify the mail settings to be used.
Go to BackOffice>>Preferences>>Email

For your contacts you can set the defaul mail settings. In most cases the defaults should work fine. That is;
Use PHP mail() function and send to both. However, if you are an advanced user and wish to set your own SMTP parameters, you can do this.
However, it is always best to select "both" as the method to send emails, this will ensure users who can only recicve text messages will get your mail notifications