According to the United States Postal Service at:

Sizes for Domestic Mail

Mail must meet these standards:

• Thickness: not less than 0.007 inch thick. Pieces that are 1/4 inch thick or less must be at least 3-1/2 inches high, 5 inches long, and rectangular in shape.
• Combined length and girth not more than 108 inches, except for Parcel Post. Pieces exceeding 108 inches, but not more than 130 inches in combined length and girth, are mailable at the Parcel Post oversized rate.
• Weight: 70 pounds or less.

Two Questions:

1. What is the maximum volume, in cubic inches, that can be shipped via the Parcel Post oversized rate?
2. What are the shape and dimensions of that container?