Watch your incoming mail every day to watch for returned invoices marked ‘wrong address’, ‘no longer here’ or ‘not valid’ address. Did your advertisements, postcards, checks, sales literature or statements your personnel mailed out come back to you? Did you get the address wrong? Has your customer moved? Did your customer go out of business? You need to know this ASAP in order to react from a purchasing, sales and production perspective. Train your personnel to watch for these items back in the mail and tell them to bring them to their supervisor quickly so your management can react. The returned item could be an invoice for a shipment that is now in question. It could be your AP check you mailed from accounts payable which needs to reach your vendor in order to maintain good credit, otherwise, you may be put on credit hold. Whatever the reasons are, call and find out what stemmed the post office to bring it back to you.