Post Office – Castle Douglas, Mossdale mobile service – Opening Hours & Branch Details Post Office is situated currently on Car Parking Area At Mossdale Store, a 8.21 mile driving distance north-west from the centre of Castle Douglas. Customers can easily come here from Kirkpatrick Durham, Parton, Airds of Kells, Balmaclellan, Slogarie, New Galloway, Corsock and Mossdale. For the day (Friday), it is closed. Please see this page for further information regarding Post Office Castle Douglas, Mossdale mobile service, including the operating hours, address details and telephone number.