Envelopes are acceptable for mailing certain items that can reasonably be
expected to be processed and delivered without damage to the contents or to
other mail or mail processing equipment.
A letter-style envelope is any nongusseted envelope within the dimensions
shown in Exhibit 2-5.2. A letter envelope is acceptable for mailing nonrigid
stationery and similar items weighing up to 1 pound and measuring up to
1 inch thick.
For an easy load of up to 5 pounds, an envelope that exceeds the letter-size
dimensions is acceptable for mailing. This large envelope should be made
from paper of at least 28-pound basis weight or from material with a Mullen
strength greater than 90 pounds per square inch.
An envelope designed as a photographic film mailer or a gusseted envelope
is also acceptable for mailing if it is made from envelope paper of at least
24-pound basis weight.
Pens, bottle caps, and similar odd-shaped items are not acceptable in a
letter-sized envelope mailed at the single-piece First-Class Mail rate. These
items can split or burst the envelope and injure Postal Service employees or
damage other mail and mail processing equipment.
An envelope may be used to mail an odd-shaped
item at the bulk Standard Mail rate if the item
meets the requirements for that mail class.
The item should be wrapped with the other
contents of the envelope to streamline the
shape of the envelope for automated
processing. The item's package should be
able to effectively hold it so that the
contents and the package will not be