Had an enquiry. Responded ultra rapidly. Had a reminder from Airbnb to answer the enquiry so ignored it as I already had. Had another one the day after so sent the enquirer another Airbnb email. A few hours later an automated email from Airbnb came back "Reservation Request Expired" telling me I would likely go down in the ratings because I didn't respond.
It's important to know the difference between in INQUIRY and a RESERVATION REQUEST. It sounds like this was a reservation request - which needs to have an ACCEPT or DECLINE within 24 hours - not just a return message.
I too have a number of messages that are titled "Enquiry". Yet I am constantly prompted to Pre-Approve or Decline. Somtimes these are just simply questions, people looking for information about my place before they book. Event if they decide they don't want to book my place, I am still prompted to Decline or Pre-Approve. This does not make sense. I get penalized for selecting Decline when they don't even want to book my place.