When a guest contacts you after they have completed a booking, a returning guest badge shows up beside their name on the Inbox thread (or in the right sidebar):

This insight is useful to hosts, since returning guests may be treated differently by way of communication. After seeing this badge, you may want to customize the guest’s messaging and use the opportunity to welcome them back.

For all returning guests, the conversation thread will remain the same. You’ll be able to view your past conversation(s) with them to easily pick up where you left off.