There are no specifications as to what box you must send your media mail package in. The only requirements are that the package must be taped securely so the item does not fall out of the package and the address must be clearly labeled on the front of the packaging. If you are recycling a box or envelope, you must completely remove the original address off the box so there is no confusion when shipping the package.
Find a box or envelope that fits the item you are sending. You want to pick a box or envelope that will securely fit around the item. If there is room for your item to move around, it could become damaged during shipping. Wrap the item in bubble wrap or with packing peanuts if it is fragile (such as a rare CD or album). Write "fragile" on the front of the box if it should be handled with care.
If you are shipping high quantities of media mail, package all of the items the same. The uniform items can be sent at a predetermined rate for bulk pieces (under 300 items). For example if you are sending 50 of the same DVDs as a promotional deal, you can send them for a discounted rate. Promotional items can be sent through Media Mail as long as they do not contain advertisements. For example if you are sending CDs to fans, they cannot contain paid advertisements on the disc, in the book or on the case.
At times people are confused about the type of box needed for media mail because other types of mail services require a specific style of box. If you choose to mail your media through First Class mail, that does not require specific envelopes either. However, if you choose to use Priority Mail, this requires a box or envelope from the post office. Priority Mail rates are based off the box or envelope used to mail the package. Media Mail gives you the freedom to package the items as you wish.