I’m not sure this author really understands how USPS works. Having spent quite a bit of time in their facilities in years past, I know there are three basic kinds of mail: letter mail, flats (i.e. magazines), and parcels. Each is handled by automated equipment that is unique to each type of mail, and thus the facility must be capitalized for each. The volume of each type has fluctuated historically but until the internet came along, the volume of letter mail has always increased year over year. Now it’s dropped like a rock. That means the facilities are overcapitalized and inefficient and adding more flats or parcel volume may help keep a P&DC or Bulk Mail Center open, but it won’t change the fundamental problem - the precipitous drop in the volume of letter mail.
Type means letter, flat, parcel, sprl (Small parcels and rolls). Class means what rate category it was entered as ~ to wit, Preferential (First-Class, Express, Priority, Periodicals ~ in part) or Non Preferential (Standard, Parcel Rate, etc.)
The names vary over time of course ~ always some new idea.
Then there's the indicia ~ stamped mail, permit imprint, metered, and franked.
Once you know the handling characteristics of each, as well as the rules regarding minimum quantities required for entry and how those quantities must be pre-sorted, then you get an idea of what costs a lot, what costs less, what can be handled such that the "next handling pieces" are essentially profitable.
Direct Mail Advertising is typically entered at the Standard Rate in letters and flats.
DMA is the big money machine for USPS. The requirements are enormous to qualify to enter mail at that rate, so the mailers' work before mailing squeezes most of the costs out of the category.
Automation has also whacked postal costs tremendously
Unfortunately the USPS did not realize much of the productivity improvement because it didn't lay off unused labor. Most of that problem was hidden under the ever increasing mail volumes.
If they'd "right sized" the labor force they'd been hiring many of them back a year or two later ~ in a normal economy. Management was always too timid to do that.
The Great Obama Recession has forced the issue. USPS now has to lay off the surplus folks.
At the same time USPS continues to handle half the mail in the world.