Could be relevant to some people here. hope its within the rules to post.
Didnt want to link to usps
On Sept. 26, the United States Postal Service announced more restrictive rules governing the mailing of packages and letters franked with postage stamps. To alert USPS customers regarding the new regulations, a new warning label is being affixed to the nation’s more than 142,000 mail collection boxes.
The United States Postal Service has further tightened its rules governing the use of postage stamps on parcels and large letters.
New Aviation Mail Security Program rules will prohibit customers from placing stamp-bearing mail pieces that are more than ½ inch thick or weigh more than 10 ounces in mail collection boxes, building mail chutes or post office mail slots.
The USPS announced in the Sept. 26 Postal Bulletin that effective Oct. 1 such letters and parcels must be presented in person at a retail postal counter.