People seem to get confused about over one ounce additional postage, and nonmachinable additional postage.
Nonmachinable Criteria
A letter-size piece is nonmachinable if it has one or more of the following characteristics (see 601.1.1.2 to determine the length, height, top, and bottom of a mailpiece):
a. Has an aspect ratio (length divided by height) of less than 1.3 or more than 2.5.
b. Is polybagged, polywrapped, enclosed in any plastic material, or has an exterior surface made of a material that is not paper. Windows in envelopes made of paper do not make mailpieces nonmachinable. Attachments allowable under applicable eligibility standards do not make mailpieces nonmachinable.
c. Has clasps, strings, buttons, or similar closure devices.
d. Contains items such as pens, pencils, keys, or coins that cause the thickness of the mailpiece to be uneven; or loose keys or coins or similar objects not affixed to the contents within the mailpiece. Loose items may cause a letter to be nonmailable when mailed in paper envelopes; (see 601.3.3).
e. Is too rigid (does not bend easily when subjected to a transport belt tension of 40 pounds around an 11-inch diameter turn).
f. For pieces more than 4-1/4 inches high or 6 inches long, the thickness is less than 0.009 inch.
g. Has a delivery address parallel to the shorter dimension of the mailpiece.
h. Is a self-mailer that is not prepared according to 201.3.14.
i. Is a booklet that is not prepared according to 201.3.16.
The bold areas are the reasons I was given by my Post Office's manager as to why the additional $0.22 is required on ALL envelopes containing an item such as a top loader. Even if you don't write "non-machinable" on the envelope, it's still required. He was honest and said that rarely they get caught, but around the holidays they catch it a lot more often because of all the greeting cards that require additional postage. Basically, from what he was saying, we take a chance every time we mail without the additional non-machinable postage and don't label the envelope as non-machinable.