Guests are allowed to request IB even if they are not verified. The restriction is only on actually booking a reservation. When someone sends an IB, you are not penalized for not responding because the default is an Accepted reservation.
For IB requests from non-verified guests, Airbnb will require them to get verified and will put the reservation in Pending status until the guest has done so.
Guests are allowed to make Inquiries even if they are not verified. The restriction is only on actually booking a reservation. When someone inquires, you still need to respond quickly. For inquiries from non-verified guests, you may want to create a standard reply with either questions about them and a statement reminding them that you will required they be verified before they can actually book a reservation.