The term MAIL CTRS refers to two job positions in the postal service. The first is POS, which stands for Postal Operations Supervisor. This position is responsible for supervising the daily operations of a post office, including customer service, mail sorting, and other duties. The second is GPOS, which stands for General Postal Operations Supervisor. This position is responsible for overseeing the operations of multiple post offices, ensuring that all operations are running smoothly and efficiently.