By default the guest will receive a booking notification from noreply@BookingAutomation.com. You can set the system to sent confirmations from your email address in SETTINGS -> ACCOUNT -> OUTGOING EMAIL.
To send follow up messages to guests hosts have the option to set up template e-mails in SETTINGS -> GUEST MANAGEMENT -> AUTO ACTIONS.
Template e-mails can be sent automatically at specific times or or manually directly from the booking.
Template Variables may be used in the email. Template Variables are special short codes in square brackets [ ] which are replaced by information taken from the booking. This allows you to automatically include your guests name, date of arrival etc. in your email.
Gmail can be used for outgoing email but you must be take extra steps if you have 2 step verification on your account. You will need to generate an application specific password as explained here: https://support.google.com/accounts/answer/185833?hl=en