Although you were not injured in the accident, you can still claim wage loss because under the circumstances you described, you cannot perform your job while your car is being repaired and there isn't any feasible alternative to using your own car for delivering mail.  The amount of lost wages you are claiming will require supporting documentation from your employer.  You can file your wage loss claim with the insurance company of the driver who caused the accident.  Compensation for wage loss is straight reimbursement.