The good news is, yes, masked booking.com emails (eg. firstname.lastname@example.org) are perfectly usable in GuestJoy.
Booking.com emails actually act as forwarding agent. Your GuestJoy emails will end up in the guest's actual email inbox, as well as guests being able to see the email content on booking.com.
What about Expedia?
Expedia is a little different; it depends how the guest chooses to pay for their booking.
If the guest chooses to pay at your property, then we can communicate with them with no problems.
If the guest chooses to pay via Expedia, unfortunately the masked email address (eg. email@example.com) cannot be used to communicate with guests; this is Expedia's universal policy.
Do your best to get your guest's personal email address
Booking.com masked emails can be used for 60 days after the date of departure, and after that time they will no longer work.
We strongly encourage our customers to collect a guest's actual email address upon check-in, or even prior to arrival by using GuestJoy's Check-in feature.