I throw most of the stuff that appears in my mailbox away as soon as I see it (the balance are bills that I would PREFER to throw away but can't). However, every once in a great while, an item of real interest appears. In the most recent case it was the very substantial Uline Corporation catalog. Although aimed at commercial shippers there are a cornucopia of goodies in here (and on their website) that are of interest to wargamers seeking an answer on how to safely store our tiny armies. They produce boxes in sizes ranging from the ridiculously small to the frightfully large as well as shipping tubes (perfect for maps) and every imaginable packing material. Whether you need twenty boxes or a thousand you will most certainly find what you need here, take a look.
Of particular interest is this page that lists "literature mailers" which are nice flat sturdy boxes with tab-closed lids, they come in different heights and sizes and will accommodate everything from 2mm to 54mm figures. I have dozens securely storing my 15mm WW2 collection.